I'd hardly consider myself a purist. I accept it all. Books, comics and others included. Star Trek is not a universe, it's a multiverse and we've known this since Mirror Mirror. The parts that contradict? They're from universe #185,290 and 59,227. No biggie. If someone wants to see Old Spock as the one from the DC comics instead of TOS, more power to them.
If someone came up with a compelling story that relied upon Old Spock being a different one that "our" Spock and if the editor and CBS agreed then we'd get that story. That's a big if but by no means one that's impossible.
Once Abrams is done with his movies we'll get another movie series or perhaps a TV series or two, based on someone else's vision of what Trek is. Contrary to some of the time travel stories, the future is not set in stone. Neither is the past. The universe exists in whatever form the current (or future) owners of the franchise say it does.
Desirable? Irrelevant as it's based on what's going to make the most money.
Useful? Who's to say what one person or the other finds useful. You may not find it useful but someone down the line could turn the idea that it's a different Old Spock into the best Star Trek we've ever seen. Who knows?