EDIT: In the first half of my OP, I listed 10 of my own suggestions, and in the second half of my OP, I listed 10 suggestions from other players in the comments I liked.
NOTE: The reason suggestions like Build Templates, Sigil/Rune swapping, a GvG system, decent PvP matchmaking, a WvW population solution, a new Engine, etc. are not on my list below is because I wanted to throw in a few other suggestions that have been brought up less often, if ever. I did not want to make a thread parroting those other suggestions. How funny it is, though, me making this Note technically puts them on the list, but anyway...
1. Unlimited Volatile Magic gathering tools in the Gem Store. It is silly how the new Map Currency Unbound Magic gets its own set of ‘unlimited’ gathering tools, yet Volatile Magic does not. My wallet is ready in the event Unlimited Volatile Magic gathering tools come to the Gem Store.
2. Allow us to see the totals of any Material we have gathered when we 'Sell' and/or 'Buy More' Materials from the Trading Post within both of the Buy/Sell Windows. Mock-up image of the idea here: https://imgur.com/zJPhbzm
Updated with mock-up image:
3. Allow us to toggle any Currency in the Wallet we want to keep track of (up to 10) along the bar where our Gold value displays in our Inventory Window, much like we do when we toggle which 'Achievement progressions' we want to keep track of when we hit the 'Eye' icon. Mock-up image of the idea here: https://imgur.com/a/urqxQ
That 'Eye' icon should be next to every Currency in the Wallet Window. Why up to 10 Currencies shown at once? Because 10 is a solid number, and anything more than 10 would look like clutter along the bar where our Gold value displays.
I also improved the idea where any displayed currencies along the bottom bar of the Inventory can be dragged-and-dropped in whatever order players want them displayed.
And if not any of the above stated, please, let us at least see our Karma value at all times since it is a globally-acquired Currency in every Map. For example, in maps like Bloodstone Fen, Lake Doric, and every other new map outside the Heart of Tyria, we cannot see our Karma value at all times like in other Maps.
4. Add the option to 'Sell' and/or 'Buy More' of any Material from our Bank, and add the option to 'Sell' any Material from our Material Storage. Currently, we can only 'Buy More' of any Material from our Material Storage. Why only 'Buy More' and not 'Sell', too?
It may sound trivial, but it is really frustrating over a period of time having to drag-and-drop each and every Material from our Material Storage into our Inventory before we can 'Sell' our Materials on the TP, and not being able to 'Sell' and 'Buy More' of any Material at all from our Bank is equally frustrating.
5. Let’s take a look at the Additional Crafting License item in the Gem Store. It reads: Increase the number of active Crafting Disciplines all characters on your account can have at once (by 4, to be exact).
Why not increase the number of active Crafting Disciplines all characters on our account can have at once from 4 to 9?
What is the difference if our mastered Crafting Disciplines are split up to be accessible on 3 different characters vs. all accessible on any character? (3 different characters because of Scribe). Just have them all accessible on any character that already has them mastered. We should not have to split our access up to our mastered Disciplines between 3 different characters. That is not effective nor convenient at all!
6. Increase the number of ‘Recently Viewed’ and ‘My Latest Trades’ up to 10 (or 20) shown at a time. Mock-up image of the idea here: https://imgur.com/IQGy88A
7. Add a Consume-All option to all consumable Finishers, because they are one of the most annoying items to 'Destroy' by having to type in their exact names. They are really only an annoyance after opening many ToT Bags (among a few other containers/bags that contain Finishers), but an annoyance nonetheless.
8. Add 'Y' and 'N' hotkeys for the 'Yes' and 'No' options when we ‘Destroy’ any item to make it quicker, or for all 'Yes' or 'No' dialogue boxes, for that matter. Mock-up image of the idea here: https://imgur.com/a/hPY6U
With the above suggestion in mind, the hotkeys for 'Y' and 'N' should be an Option in the General Options Window, to Enable or Disable them, either to appear in 'Y' or 'N' dialogue boxes, or not appear at all in 'Y' or 'N' dialogue boxes, followed by a red warning message in parenthesis ( ) next to the Option itself that says, "Use at your own risk!"
9. Add a World Boss Events Window (within the Contacts and LFG Window) so we do not have to alt-tab and consult third-party online sources outside the game. Mock-up image of the idea here: https://imgur.com/hd2zuWW
NOTE: If you look at the UI mock-up closely, you will see I put little 'sort by' arrows next to 'Boss Name', 'Boss Level', 'Event Status', and 'Spawn Time'.
Some players do not mind alt-tabbing to their web browser every time to consult third-party sources for when World Boss Events pop, but having a World Boss Event Window within the game itself will be better. Such an Event Window should have existed a long time ago, anyway.
10. Remove 'global' cooldown on all instruments and instead make it where each note has its own cooldown, and then set every players' 'Player Instrument Volume' to 2-5% after this fix to lessen 'annoyance' from obnoxious players. However, if not to remove the 'global' cooldown on all instruments, then at least remove 'global' cooldown on the most popular two instruments being the Lute and the Harp.
Currently (to use the Harp as an example), if any of the lowest Major notes: C D E F G A B C on the first octave go on cooldown, so do any of the C D E F G A B C Major notes on the second and third octaves, meaning each note does not have its own cooldown. The cooldowns on instrument notes are shared 'globally'.
To be clear, even if 'global' cooldown on instruments is removed, troll players are not going to be able to spam hundreds of notes in the event they used a script to do so, because each note on any instrument at that point will have its own cooldown.
10 SUGGESTIONS FROM OTHER PLAYERS IN THE COMMENTS I LIKED (with very minor changes in wording)
1. Ziooo.8932 suggested: No Mastework Sigils from salvaging on high level Armor [Levels 40-80], because who uses Masterwork Sigils after level 40?
2. Ziooo.8932 suggested: No Armor breaking, but only in Raids and Fractals, since it is auto-repairable, anyway.
3. Ziooo.8932 suggested: Make every refinement (Ores, Cloth, Wood, Leather, etc.) available on every Crafting Discipline.
4. STIHL.2489 suggested: Allow us to Glide in Dungeons and Fractals.
5. Orpheal.8263 suggested: Add the final implementation of Jeweler and Chef 500 to make them equal to all other Crafting Disciplines.
6. Orpheal.8263 suggested: Do a complete rework of the mess that is the whole outdated 2012 Condition and Boons System to a more modern and adapted system that works with the current state of the game.
7. Orpheal.8263 suggested: Quick-use Slots, which enable us to use items from our Inventory except without having to open our Inventory during combat.
8. STIHL.2489 suggested: Allow us to use Mounts in WvW (Edit for movement purposes only, and disable Mount attacks for balance purposes since they single-handedly deal 3400-4K+ dmg, depending on the Mount, in conjunction with certain Buffs they provide either to the player or other allies that would stack too quickly).
9. Ziooo.8932 suggested: Allow us to Glide and use our Mounts in our Home Instance. To which I replied, "Why is Gliding and Mounting disabled in our Home Instance, anyway?"
10. Orpheal.8263 suggested: Implement more fun and useful Emotes.