CAPI is "open" solution to do the same thing, though NVLink supposedly still offers more bandwidth. Unfortunately CAPI is only available on POWER8 hardware at the moment and I'm not sure if IBM is open to license it beyond OpenPOWER - still, there's a decent number of CAPI-capable cards already available and more coming to the market in the future.

GPU's may not be great for every unit of work a RDBMS has to perform, but given their ability to rapidly compute hashes it could help a lot with joins (as evidenced by PGStrom).