Correct me if I am wrong but you want to completely remove conjured weapons for permanent weapons?
I'm not trying to be rude, but I think your idea is superfluous. Why? Because it's happening already without the need to remove conjured weapons (the Catalyst hammer and the conjured lightning hammer for example). They already said that they are working on a new expansion which will most likely come with more elite specializations which means more weapons, which also means that we will be getting a great sword, or longbow, etc.
I might not have written it clearly (my bad) but you would only conjure a second weapon if you have the Conjurer trait selected. This would be passive, no need to use a ground target as the weapon would drop at your feet.
Conjurer weapons already disappear after a certain amount of time whether it's picked up or not. This mechanism exists currently.
The idea I had about the weapon disappearing (or becoming useless) after skills 2-5 are used up would be the same as the bundle item Koda's Flame. This mechanism also exists. My thought process behind this is that no other class should as proficient with conjured weapons as Elementalist.
I think it would be more of a hassle add a batch of permanent weapons to the game because they would have to design the other element skill sets from scratch which are currently nonexistent (water great sword skills for example).
Switching elements would work as it does now; no effect on the conjured weapon skill set. If you need to use earth skills just switch back to your normal weapons and if you want to use thunder hammer again just switch back to it like a Engineer would do with the flamethrower kit.
There is also some synergy with switching elements with the Catalyst. Using the thunder hammer skill 1 combo to create different auras every time you drop fields using the f5 skill is pretty fun and also works well with traits that grants you and others boons and auras.