Good news : 10.9 has best support yet for Titan, including OpenCl.
Bad news: If you think that there will be many 3rd party GPUs, you are dreaming.
Why was EVGA able to offer GTX285 and GTX680 for Mac? Simple, they are 100% identical to PC version. The 680 literally is, and the GTX285 is just missing an S-Video port and has a different EEPROM. So, same assembly line, no retooling, no special parts. Different story with these new cards.
The demand will be HUGE due to inability to run anything else, so maybe the ability to charge $800 for a single GTX770 (and you would need 2) will make the demand big enough to make the boards.
But you won't be driving to fry's and getting a PC card and booting up.