What they need to fix in a few cases isn't an overhaul, it's literally a hotswap.
G2 is forked into Dawn. Dawn is amazing. They could potentially licence/buy/acquire/magic/steal some work Dawn had done on it for DXMD. They don't need to apply their own staff to much beyond fixing it, or the game could become a joint thing between EIDOS and IO, thus potentially bringing in DXMD fans with the news.
This is basically what G2 seems to be based solely on not poking around the binary beyond dumping strings. There are at least a dozen libraries referenced by name.
OOooh I do, pick me
They basically need to merge Dawn back into G2 to fix a bunch of bugs cheaply. We're talking what are most likely component based upgrades (looking again at only the game data files, and how I can get them to load in the other game).
SE might, but I'd imagine IO would like to stay in business.
The best way forward, IMO, and my absolute desire, would be to see this become an IO+EIDOS game again, even if that means EIDOS fix the engine and IO do the story work. EIDOS still have a firm, amazing, reputation; IO's has basically fallen off a cliff in the modding/RE world. I couldn't find any of my old contacts who owned Hitman, or even considered picking it up, despite liking the old ones (and having modded a few of the old ones with me). Part of that is undoubtedly due to a horrible game being released in the series (I speak of course of Blood Money, which a lot of people did not enjoy; not Absolution, which from a modder's point of view is amazing). Anyway, that's opinion territory, and best left out.
The bottom line is something drastic has to change in the engine. I don't have a huge amount of faith in what's coming, but I've stuck it out for the season in the hopes that by the time season 2 lands things are better.