You are being unnecessarily pedantic here.
I don't know what national leadership has to do with game mechanics.
Bards have a niche of their own. Some of their spells may overlap, but the bard's niche is unique: they get their magic from music.
Psions are, in terms of flavor, mostly identical to sorcerers, since both of them get their magic from their own bodies.
I find it highly unlikely that there will never be a 6e, unless humanity dies out first.
That's on your DM, then, not on the game.
Also unlikely, since people are less likely to buy something if the mechanics are bad--especially if the mechanics are the core element. It's not like a setting that you could use with a different system. If the psion has pretty themes but doesn't play well, it's useless.
In a fantasy game, it's not irrelevant. A lot of people don't want science fiction elements in a fantasy game. I don't. So if the Voidrunner psion feels too sci fi-ish, I wouldn't allow it in my generally lower-fantasy games.
I don't recall there being multiple versions of the artificer being touted. Also, the artificer was built primarily for a specific setting.