I don't think Riecoin is mineable by GPU. I expect it to be sometime, but so far I'd say it isn't.
I briefly looked at feasibility. My better half mines primes based coins (exclusively) and wants to mine riecoin, but she basically only GPU mines. (She's been bugging me about making a cuda/opencl miner for constellations since hearing about your coin while we were discussing Tetriscoin theory.
)Recently, I learned a neat trick for gpu memory management (basically an extension of some work from an ACM journal about optimizing "dynamic" allocations for linked lists) that I think might be particularly applicable so I might revisit it before too long.
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I think the cpu coin list here is fairly accurate: http://cpucoinlist.com/
I'm surprised MOTO is not on that list.