The only restriction is that they have to keep their modifications open source
And since it’s GPL that any additions are compatible with the GPL, which the ad / tracking stuff they’re likely to add likely isn’t.
And if all development effort moves to the fork, Zipo can still take that fork and redistribute it under the “Simple Mobile Tools” name.
Only if they don’t add their own proprietary shit, and if they don’t, how would their “bully users to pay for features” business model work?
According to github.com/SimpleMobileTools/…/241#issuecomment-1… “like 99% of the current code has been written by me and other paid devs, so no need to overreact the licensing thing” it seems like the remaining 1% is going to be ignored or possibly even removed if they think that leaving that in might open them up to DMCA claims by disgruntled contributors - which taking code from an open source fork would definitely do.