It is still possible, though more difficult. I tried soloing it shortly after hitting the level cap and couldn't make it past the second encounter. However, after gearing up some more (I'm now at 17k item level, starting to fill out with ME gear from Undermountain) I was able to make it to the boss on my own as an arbiter cleric.
The fights are not easy, and I died two or three times on the way, but I did make it. Farming the two wyrmlings isn't nearly as fast as it could be, since you actually have to fight them instead of merely slaughtering them. I'd estimate it took me about 30-45 seconds in between pulls to kill the pair. I stayed there for about 15 minutes and got my 50 kill trophy. (didn't check how many I had before starting) When I took a break for dinner, found out that you will be kicked from the instance if you stay logged out too long.
Definitely not as easy as it sounds like it used to be, but still better than any other method I know of. I'll be devoting a few solid hours of grinding over the weekends from now on until I hit the goal.