I agree with others that the ship has sailed as far as this being a legitimate dream match goes. Plus, Taker's time is limited and with only maybe two or three Wrestlemania matches left in the tank, I'd rather see them spent in matches and feuds with the likes of Lesnar and Cena than with Sting.
To me, this match would have been best if it had happened during the WCW Invasion storyline (or even after) because there's similarities between the two guys as far as being the "consciousness" of WWF and WCW goes. Undertaker and Sting were the ones who were the most ferociously loyal to their respective companies and were pretty much the two principal guys you could point to in either promotion who you could count on never jumping to the competition and neither ever did. That would have been a cool thing to market their feud around (it wouldn't feel as special harping on that kind of stuff today.) The fact that their gimmicks wouldn't have been as compatible at that point (due to Taker playing his more humanized American Bad Ass persona) wouldn't have really mattered because Sting's Crow gimmick was hardly mysterious anymore by that point either. He wasn't the silent warrior who stayed in the shadows any longer, he had already become just like the old Sting once 1998 arrived, just in different face paint.