Frost_BiteLightning gun for solider would probably be a little too good. It would have to be considerably nerfed to be balanced and then no one cares.
I could, however, see a plasma gun for soldier secondary. Wouldn't be OP and can do fun jumps!
assuming that it works akin to the SMG, it could work sorta. Like if you had to hit 2-3 shots after nailing a scout with a rocket, and ended up with a noticeably longer TTK, it could work as a jump denial weapon or whatev or just a mildly better long range spam weapon
The general vibe valve has had with updates, as well as the commentaries tends to suggest that they want to avoid any Assault rifles or SMGs for the main combat classes in order to keep the game more unique or something tho, so prolly no LG ever :(