Fixing instanced missions so they scale to level and team size like they did in CoH would do a lot more to make the game appeal to me, personally, than one trial would. The various Adventure Packs already do, so it should be doable.
I just want to be able to run through normal content without it becoming trivially easy the moment a second player appears, and without it suddenly being three levels lower than me if I go do something else for a bit. Is that so much to ask?