Well in a way I guess we're discussing the same thing -- but that DSP card already exists in the form of a graphics card that isn't used during most folk's music making.
It's not a "no-brand" solution in the sense that one vendor supplies the graphics cards, but as far as I know the software SDK for CUDA is completely free/open and available to anyone... I see lots of hobbyists working with it... example here:
http://www.theover.org/Cuda
There's also a tremendously flexible range of power to choose from among GPUs. You can pay $50 for a graphics card or you can pay $1000 depending on how much processing power you want (i.e. think plugin instances). You can buy one of them today and add a second or third later and scale linearly. The guy above is working with low-end (by today's standard) GPUs and getting results.
Now EvilDragon's position is that there are technical reasons that some types of audio applications won't work on CUDA, and I'm not completely denying the possibility, I'm just looking for answers to what they are that I can digest, because the evidence I see seems contrary.
As far as someone coming out with a card that is not proprietary and is designed for open use.... well the problem there is the level of R&D required to produce the hardware and software to do something like that is insane... tens of... no probably hundreds of millions of dollars. If someone invests that kind of money, there needs to be some return in it for them, they cannot just invest it as an act of goodwill to give to the community.
So we end up back at the folks like TC Powercore... someone there bit the bullet and invested some money and took a gamble. Apparently there wasn't enough money in it for them to sustain.
So I think what we are more likely to see are less-ambitious, specialized devices utilizing DSP. Actually that's all the Ultranova is, a DSP with an audio interface and software plugin.... but for a few more bucks why not add keyboards and knobs and call it a synth. Much cheaper to support a single-purpose hardware synth than a complete computing platform like CUDA.