Everyone is free to contribute whatever code to whatever project for free. But, regardless of whether it's Haiku's donation monies or Google's, you shouldn't pay for code that you wouldn't be willing to use the Haiku money on if you had a little more funding.
All that's been confirmed now is it's okay to waste Google's money IF your proposal is spiffy enough AND you won't be wasting any core developer's time.
I think the core kernel developers have felt like pigs in slop for years. Release? Get the next nightly build. THERE'S your "release"! There's no purposeful direction from that herd of cats or else the forward pacing wouldn't have been so glacial. Linux has viability because it has commercial application. Haiku has no such aspirations but that's what you need to get orders of magnitude of world interest.
It takes more of a rich userland development experience like NodeJS and Mono / .Net Core / Web to get noticed at the level where you're going to get attraction from a whole set of programmer's who could care less about what the next kernel tweak is. But you need those kinds of developers to drive demand. They're the ones driving kernel changes, not the other way around.
Haiku is exactly where it is because the core kernel developers are happy where it is. I didn't know Phipps but he seems to have seen this coming from miles away.