Yes, you can boost your Char to Level 30 to start WoNY immediately, once you finished the WoNY campaign, you can get back to DC.
BUT, AFAIK, boosting your Char will complete the DC story, so you can just replay the stuff instead of doing the whole story and side missions.
Lol, at this point, once you've played the WONY story, they should just let future new characters start right at 40. I mean......what truly, is the point of makin us play the WONY story over and over?