Sony disabled Other OS in the 3.21 firmware update

I would advise against buying a PS4 until Sony restores that function as a sign of good faith.

The PS3 would probably fare no better than a GPU mining. If you want to mine, you essentially need to invest in ASICs. If Sony still had other OS, you could probably use it to control the actual hashing machines. The 256MB of RAM would be limiting though. (For using P2Pool you essentially need 2GB to run P2Pool and Bitcoind at the same time).