The BUSL license requires shifting to an open-source license no later than 4 years after publication. I'd be happy to contribute to a BUSL-licensed project knowing my contributions will shift to an MIT license within 4 years.
And the original authors don't have to worry as much about Amazon eating their lunch.
While that is certainly better, the original point still stands. If the company goes bust the latest source code will only be open source after 4 years. By that time other software has likely taken over the need in the first place, because not having that need fulfilled for 4 years is mostly not reasonable. And older versions often don't have compatibility with new versions either.
A bankrupt company will try to sell the rights to the software. If nobody buys it, and it's completely written off the balance sheet, then most likely they will just flip to an open source license ahead of schedule.
And if they don't, 4 years isn't that long to wait for something that nobody wanted to buy in a fire sale anyway. Especially if you're free to use it the entire time, just not resell it.
Good for you; you seem like a trusting person. I'd recommend against spending your time on that. Or at least try to get paid for it.
I tend walk away from anything with a shared source license. I don't invest my time in it. I don't finish reading the README. It's an instant red flag.
"Effective on the Change Date, or the fourth anniversary of the first publicly available distribution of a specific version of the Licensed Work under this License, whichever comes first, the Licensor hereby grants you rights under the terms of the Change License" ... "To specify as the Change License the GPL Version 2.0 or any later version, or a license that is compatible with GPL Version 2.0 or a later version, where “compatible” means that software provided under the Change License can be included in a program with software provided under GPL Version 2.0 or a later version"
And the original authors don't have to worry as much about Amazon eating their lunch.