First, using Rust does not in any way mean that you’re forced to use pushover licenses. I license all my Rust code as GPL.

Second, I hate pushover licenses, but I don’t see GPL projects using pushover licensed code as a problem. You’re essentially relicensing the pushover licensed crap as copyleft, which is a good thing. Any improvements that they make to MIT licensed stuff will only be available to other copyleft project, thus making the base MIT stuff less appealing.