Have there been any discussions about upstreaming this into cargo proper? Are there any significant downsides to nextest compared to its predecessor?

The How it works [1] and Why process-per-test? [2] pages should answer your questions.

Ah, I see. You're aiming to become the hashbrown of testing.

	▲	sunshowers 3 hours ago \| parent [-]
		Oh gosh, were we to be so lucky :) just aiming to solve problems my coworkers and users see, and doing it with care, is all.