I suspect this would be a very risky proposition for them. The expense would be enormous, so it would either need to be a player with such huge economies of scale to make it work, or it would have to be a collection of businesses that in aggregate could make it economically feasible. I would suspect in most cases, it would be a lot cheaper to just port your software to modern Linux than to try to get react OS over the line. And that's before considering that a lot of the large players will be in contract situations with Microsoft that likely directly prevent this sort of thing

There's a sponsorship section but it just links to the donate page rather than a corporate focused sponsorship program. It seems most of the corporate activity in this space is around userspace compatibility rather than NT kernel compatibility, like CrossOver or Valve driving Wine and other codebases in that regard.