This is a really cool idea, even if it could take away incentives to explore/crunch lesser known projects. Ideally we could even use this sort of system to encourage people to retire super old systems.
(e.g. there are still 450 Pentium 4 systems actively running BOINC)

However, there are bunch of annoying issues that I've come across while working on QuickMag, that could present serious problems for calculating M fairly.

Potential Issues:

• BOINC CPU credit is based on your whetstone FLOPS score * task run time. However, this doesn't take advantage of more modern CPU instruction sets (AVX and its successors) that do significantly more work per cycle.
• Extending M to account for GPUs is going to be a serious challenge. The coprocs field is a mess, older AMD GPUs are basically indistinguishable from each other, and multi GPU systems in general.
• Need to still be able to account for variation in performance due to different memory configurations/modifying CPU clock speeds.
• Currently, even without monetary incentive, there are still a few hosts that falsify their CPU/GPU names.