any chance of apple bankrolling this lawsuit on behalf of arm/softbank?
Why? How does Apple benefit?
Qualcomm having a core that's competitive with Apple does not hurt Apple. People haven't been switching from Android to iPhone due to performance, there wouldn't be a switch back even if Qualcomm had SoCs that were better.
People also aren't buying Macs because they are ARM, but some (unknown) number of people are NOT buying Macs because they are ARM - the people who need to run Windows stuff. This was feasible with x86 Macs, and while possible with ARM Macs it isn't a smooth process and currently isn't supported by Microsoft so no enterprise licensee would consider it.
Having ARM PCs that were a match for x86 PCs (ignoring the high end stuff like AMD's model X and Intel's model K that people here think matter so much but 95% of the market doesn't care about) would force Microsoft and Windows devs to support Windows/ARM on an equal basis with Windows/x86, which would be a real positive for Apple selling the Mac to the enterprise market.
I agree with poke01 that Apple will not get involved because no possible outcome makes any difference to their perpetual license, but if they did I wouldn't be so sure they'd be rooting against Qualcomm.