It's hard to say - MPEX only appeals to startups involved in the Bitcoin space. Traditional startups have traditional VC funding routes, and larger companies have larger domestic exchanges they can use. A more likely scenario than a "legitimate" company listing on MPEX is that something like Van Ads or MiniGames is a rousing success, and that is a catalyst for other "legitimate" companies.
Sure one of MP's companies could be a success, but we have yet to see a single shred of evidence suggesting he can run a company and/or turn a profit. Sure, we know he can collect massive trading license fees and create a decent options robot to take money from shitty gamblers but running an actual company has yet to be seen.
So far we've seen:
S.MG, a videogame company which looks like a 1 man operation + MP with ~$5,000,000 and none of it has been spent on developing the game. The game looks like a pre-alpha version of runescape classic at best. Unless they completely stop what they are doing and hire a competent game development team I don't see how this game can be a success.
S.NSA is another 1 man +MP operation with a bunch of money but nothing to show for a years worth of work.
VanAds looks to be yet another 1 man + MP operation which is basically a clone of adbit.co.
S.WoL is the 5000th gambling site to be invented and for some reason needed 500btc to run their site, but I do have to give them credit for not being co-owned by MP.
S.WoL is co-owned by MP.
You didn't mention BitBet (also co-owned by MP), they have a functioning website which does thousands of bitcoins of traffic and turns a profit most months.