Vod viewing on twitch is also a pain, ads every 10 minutes, buggy playback, and vods don't play in order.
What's going to happen is anyone currently storing their playthroughs on twitch is now going to export to youtube. So I guess they want youtube to get the ad rev.
So you'd hit the limit after 600 ten-minute videos, or 100 hour-long videos.
The limit also seems to apply to "Highlights" and "Uploads" but not to "Past Broadcasts", "VODs" or "Clips" for added confusion.
One might imagine this is just the logical followup of them adding that horizon initially, basically saying "the 1 in 200 of you who circumvented our policy, no, for real, stop that."
In this case, they seem to be saying long-form archives aren't helping their business and are very expensive.
Of course, since that also de facto means people start pointing to their YouTube pages as their content archives, that means they think they have such a better platform for live content that they can survive people doing the calculus of "well, if I have to host my old content on YT anyway, why am I using Twitch if I'm just going to upload to YT after..."
Whether that's true or not, we'll see. (One might argue this is a given comparing the number of people I know who stream on Twitch versus YT, but Twitch is also the place that thought people wanted them to integrate a game store in their desktop app, and appears to have the attention span of a squirrel in long-term platform initiatives, so...we'll see.)
(I work for Google, I've never worked on anything related to YouTube, opinions my own.)
In practice though I doubt this makes a huge difference either way, the vast majority of the people that can have noticeable amount of views on such already have their YouTube channels or other venues they are also making money from.
Tell user "stop that".
Highlight one hour per week, or even half an hour per week, and you'll fly right over that limit.