And I don't see how this middle way is any better for most YouTubers anyways. The reason some YouTubers get demonetized is that advertisers don't want to show ads on certain types of content. If advertisers don't want to show ads on a video through YouTube, they probably won't want to do that through this third party service either. For large YouTubers it can certainly help (which is why they are already doing it) since advertisers can seek out large YouTubers who have a fanbase matching their requirements, but I don't see how it helps in general.
With current YouTube, any fees paid in by advertisers are theirs to do with as they like, and payment-of-content-creators is just a nice thing that YouTube happens to do, but can not-do on a whim with no ill effects. "Revenue from advertisers" and "expenses paying out content-creators" are two entirely independent lines on their balance sheet.
In this alternate model, the money they would receive from advertisers would now be a liability on their balance-sheet, something owed (except for the fraction taken as fee) to the content creator, just as if it was money in a savings account they were holding for the content-creator.
YouTube content creators have responded to the flaws in this model by choosing a better one: one where advertisers pay them directly; they put the ad directly into the video; and YouTube isn't involved.
The production side of this alternate relationship is a big hassle, though; it's like it's the 1930s again, when the actors in soap operas would stop to advertise soap.
It'd be very easy to build a "middle way" where the platform handles inserting the ad creative into the video, and handles payment processing between the advertiser and the content-creator, and even captures view metrics to allow the advertiser visibility into their spend—but where the platform doesn't decide which advertisements run on which videos (with that instead being entirely up to the advertiser and the content creator to schedule between themselves.)
Yes, insofar as Google is an ad-tech company, that distributed-ad-auction is their business model's secret sauce/moat, and I'm suggesting they just throw it away. But in this case, the "tech" part of ad-tech is precisely what's killing YouTube as a monetizable platform. Content creators just need ads, not ad-tech.