Are there plans for a standalone GPU miner or this will be community responsibility to implement one?
If I understand correctly, the mining algo which Zcash gonna adopt is designed to resist against GPU and ASIC. A GPU is consisted of thousands of cores running in parallel. If Zcash team set the parameters of Equihash to make the requirement for each mining thread is 1GB of RAM then GPU mining would be a waste of electricity. So, I doubt anyone would bother code a GPU miner for Equihash.
So what can we use to mine Zcash, only CPU? I don't think it's a good idea.
There is more information on this thread: https://forum.zcashcommunity.com/t/gpu-miner-to-be-released-optimizations/538