1 Ew no. They'd end up just being turned into generic mechanical tank-like things, probably, like most of the Society ProtoMechs are. Improving current art an designs, that's OK, redesigning not. TROPrototypes art for the Procyon Quad, Minotaur P2 and Svartalfa is pretty good, animalistic and monstrous. The Hobgoblin, Sprite, Boggart and Satyr-XP are good examples of what the ProtoMechs should not be.
3 I would argue they make more sense for the Clans than vehicles do. Individual warriors, low resource cost, supporting roles, yet sufficiently mobile to keep up with 'Mechs without needing additional transport (unlike Battle Armor).
2 I suppose the ruleset could be adjusted to allow them to take roles of vehicles better at certain things.
Also they should be more available. As it is, by the Dark Age, only the Hell's Horses and Ravens use them, and neither is among the most played Clans. Kinda hard to play units that aren't available. Yes yes, "whatever works in your table" and "it is BT, salvage" always apply, but for anyone who likes sticking to canon closely, those aren't really options.
I play Wolves, Falcons and Nova Cats. Of these, basically only the Nova Cats use ProtoMechs, but only early on and with rather pitiful selection. Very disappointing.
They are "unavailable" because they didn't catch on with the players.
They didn't catch on with the players because the artwork style wasn't popular...because they don't have a niche or purpose in game...because the ruleset is a bit bland.
But CGL are a bit hemmed in here. For example, one of the issues is that BA and infantry are more effective than they should be. But that means you have BA that is better than many lightweight Protos. CGL are unlikely to address this issue by depowering BA so that removes a lot of the utility for lightweight Protos.
The art is subjective, but while distinctive, it never took off. Personally, I love the Minotaur and Roc and the Centaur and Satyr are OK but the rest are meh.
And so on. Overall, none of the issues...by themselves...are truly major. But it's when you put them together that you get players that are unexcited.
As it is....the IS Clans basically drop them by 3100, the Cats a lot earlier and they are fading from the Ravens and Horsemen. I can't think of any viable way to "save" them.
What you'd need is to depower infantry and BA to open up space and functionality for Protos. Not gonna happen.
New art? Might work...but probably not enough by itself.
New ProtoMech rules? The original ruleset apparently had them as a lot tougher but they were toned down in playtesting. Too tough however and they start crowding out Mechs the same way Protos are crowded out by BA.
A new gimmick? You have players who love Protos, but most players seem to find them unexciting and rather dull. Pedestrian. Generic. Workable but with a low cool factor. Would a gimmick of some sort give them a niche, give them that WoW factor?
How about ProtoLAMs? If the Ravens adapted LAM technology to Protos, would that work? Or ProtoQVs from the Horsemen? Something else?