Short Answer/TL;DR:
As much as I want to say yes, eh...I'm afraid not. It'd take a massive restructuring and rethinking of the game to make a stock mode work and I just don't see that happening.
Long Answer:
IF there were a BV (Battle Value, for folks who haven't played tabletop Battletech) system AND it were accurate, you could match teams of IS stock mechs against smaller teams of clan mechs. Setting a hard count at 12v10 or 12v8 would not work, because total team BVs would be fluid on a per-match situation depending on what mechs everybody brought and to have balance you'd need variable match sizes. With units/premades who want to drop at specific strengths, how do you manage that? You have a clan 12-man ready to drop but you zone in against IS so now you have to ditch 4-5 guys to make it a fair match? I don't see that working well.
Alternatively you could change the drop deck tonnage limit to a drop deck BV limit, but you'd still have to redo match size because 12v12 would restrict clan mech choices to equalize BV between teams (way worse than they're restricted right now by their lower drop deck tonnage, entire classes of mech would potentially be ruled out). That or Clans would just have fewer mechs, 2-3 waves instead of 4. Which would create a whole host of other population issues related to things like how many bodies it takes to fill out IS teams vs Clan teams, how much money it takes to put together a drop deck, etc.
Now if you made it so that IS just fought IS and clans just fought clans in this stock mode...that could maybe work to a degree. But there'd be a meta there too, and I'm certain it would be far more restrictive, especially for IS as a lot of the clan mechs have good hardpoints in general.
The FP meta and indeed the wider MWO meta is mobility/speed synergy, high-damage alphas, high hardpoints and uniform weapon profiles (aka boating). The current system lets you more or less control all of those things except hardpoint locations, and even that to a very limited degree based on which hardpoints you decide to put your weapons in, so you can bring mechs with not-quite-optimal hardpoints and still do alright if you're decent as long as you have the right speed and loadouts. Though not as well as if you'd gone full-on meta, and that's why it's the meta.
The 'stock' meta would consist only of specific mech variants that have all of those things. I really don't think we'd see anymore variety in stock mode than we do currently. Which doesn't make a stock mode unfeasible in and of itself, but I see stock mode linked to greater variety in a lot of posts and I just don't think those two things go together like that.
12 stock IS mechs vs 12 stock clan mechs, as currently implemented in-game? Nah. If you think clan has the tech edge now, wait till IS has to say goodbye to:
1) Pretty much all assaults (not fast enough)
2) Speed in general, IS average speed tends to be around 64 for mediums and heavies
3) Alphas that can compete with the clans
Do I think there are conditions where a stock mode could work? Yeah. Would I play it under those conditions? Sure. Do I think it's realistic to expect the necessary changes to meet those conditions? No. Would I trust PGI to implement these changes properly? No, and to be honest I can't think of a dev studio I WOULD trust to get it right. Would I want to make FP as a whole stock only? No way.
But this entire discussion is academic in the face of the population issue. As in it's barely enough to support the single FP mode we have right now, divide it further and watch the wait times skyrocket causing even MORE people to get fed up and leave, tanking the whole mode.
EDIT: A final note from a lore perspective. In BT lore, IS didn't win the Clan Invasion and won only a handful of individual battles. The Clans were stopped at Tukayyid (because of basically a cease-fire to buy time) but they kept the planets they took. Also, ComStar wouldn't have won a war with them anymore than the Successor States could have. In that respect the idea of balanced play in FP as a whole is very non-lore, and if FP were lore-consistent along those lines I doubt many people would stick around IS-side to get their faces stomped repeatedly...although who knows.
Edited by The Errant, 15 February 2017 - 06:53 AM.