Currently the biggest issue in the playability of WvW is numbers. Without people you can't fight larger blobs. The game gives you the outnumbered buff as a consolation of being a punching bag for the larger zerg. To combat this without breaking the game I believe that the outnumbered buff should give a +3 (or more/less) target cap to all abilities for that server on that map. This means healing will hit more allies and damage will hit more enemies). What this immediately does is remove the invulnerability a larger zerg has in stacking. This does not give the smaller group a dps buff in the way you might think. A group of 15 will still be running into a group of 30+ in this scenario. That larger group has more utilities for a fight (portals, stealth, pulls) and more healing and damage dealers. A larger group still has more dps and more healing per second. That means the smaller group cannot dps down targets as fast as a larger group all pumping numbers at the same time. This target cap buff will allows the smaller group that can outmaneuver the larger group to be able to deal damage and generate downs when getting a good engage.
Currently a smaller group can get the drop on a big zerg but they wont get downs or finish them since the aoe cap on abilities with multi hits (which make up most of the best damaging abilities in the game.. Reaper 4) do not hit the same person for all the hits in a tightly stacked blob. allowing outnumbered buffed players to hit more people will generate more downs but they wont have more abilities being casted as a larger group so they will still run into the issue of finishing those downs. This allows engaging gameplay where larger groups choose to res the downs or fight the group and I hope you can see how this scenario can play out in either teams favor based on the commanders calls. So what this outnumbered buff change would introduce is higher skilled commanders. There is no more ppt relaxing when a smaller outnumbered group still has the ability to wipe your 50 man. That small group still has a huge disadvantage. The larger group just lost their invulnerability. That's pretty much what this change I hope would do.
This would also buff server coverage indirectly. People don't play with the outnumbered buff.. they just stay logged in to farm pips and flip camps/towers to refresh the 10min participation timer. But with this change you will see guilds and players awake in these less populated time zones group up and run tags trying to fight. I bet there are already groups out there but they just wont play since they see it as they have no chance (which they really don't) and instead move to BL's and ppt. This change could also encourage groups that want to prove their prowess at the game to transfer to servers that are dead during their timezone and run small groups with the outnumbered buff and fight map q's. Overall it would see a lot of potential engagement.
The final thing about this would be a change to the way the outnumbered buff might be applied. I'm not too familiar with the ratio of players needed to have it show up but I just wanted to get this idea out there.
Other potential ideas- (LESS SERIOUS AND NEEDING A LOT OF BALANCING AND PLAY TESTING)
Something along the lines of changing the way runes work and make it so that holding runes on a BL adds a +1 target cap to abilities SERVER WIDE(all maps for that team). So if you hold all 3 your server has a +3 bonus. But the amount of players needed to do that/ the coordination would make it worth that reward Also it gives roamers and smaller squads something to do on reset in addition to running as flanking groups. This would also reduce the amount of tower humpers. If a server wants those runes they have to get out of tower and fight for those points. It could add a lot of fighting in the middle and reduce the hate stealth characters have since most of the fighting would occur away from towers with the massive reveals. Now the issue this idea introduces would be: What happens when a server that is already massive and outnumbering a another group holds all 3 runes? Simple: give the outnumbered buff that applies to the smaller server immunity to the runic buffs coming from holding BL runes. So the new outnumbered buff would give players on that map +3 and immunity to the other servers that are holding runes and gaining target caps. (this idea would need the most balance and is less serious. I would consider the first half of this seriously. I just wanted to add this into my post since I decided to share my thoughts anyway. I understand I am one person and not on the balance team. I just hoped to give someone ideas and they can take it and run with it however they want)
I hope this starts a discussion on potential changes that we might see post 3rd expansion.