What's wrong here with many of the guesses people are making though: They think simple open standards are enough.
It's a lot more than that. Don't alienate the market forces that also need to move to make this work. Too many coders write off the real business incentives side of this.
Viable competition will come from multiple vendors and possibly backwards compatible/interchangeable standards that don't require many changes in code. Give me a path forward as a vendor. Show me the money. Put code out there and maintain it/keep it up. Show me it's going to stick around.
It's like any SAAS you'd pay for or an IDE you invest in, vendors want to see an ecosystem that fulfills a set of requirements and allows them to get work done for their customers.
Right now cuda is still that best tool. I covered what will likely need to be considered in my parent post so I won't reiterate that here.
I only ask that folks don't assume that "open source linux drivers and open standards and 1 open source framework with opencl support" are enough to unseat nvidia. The market won't move for that.