I spent a bit of time on Test today with some older copied 50s that hadn't run Ramiel's arc and went a few rounds with Trapdoor. I can't discern any difference between his past incarnation (pun not intended) and this one in terms of difficulty.
Some tips:
Killing his bifurcations as they spawn should be your first priority. If you fail to do so you make the fight much harder than it needs to be. He seems to spawn one at the battle's start and one every 30 seconds thereafter. They're minion class so they shouldn't pose too much of a problem. Tracking them down can be, though. You'll want to retain your mobility throughout the fight.
If you have a damage buff like Build Up, don't waste it on his bifurcations unless you can one-shot them and get back to Trappy before it wears off.
Inspirations are your friends. Purples and reds specifically. Don't grab just one or the other.
If all else fails, swallow your pride and ask a friend to help. Hell, ask a stranger. You'd be surprised how many helpful people there are out there. Not every build will be able to solo him, it's just part of the design of the game. Having another person on hand means one person can kill the bifurcations and one person can stay on Trapdoor.
UPDATE: So I found a way to make the encounter even more challenging: play it on an SO only toon I have mere minutes of familiarity with. During the closed beta testing of Dual Pistols, characters created with that set were bumped to 50 and given the cash to buy SOs. It turns out I had a DP/Mental Blaster sitting at 50, so I decided to send him against Trapdoor. However, I had to set some parameters. Already I was going in handicapped, with little knowledge of the powersets I was using (I haven't yet played either set to 50) and only basic enhancements, but Mental has a -regen debuff in Drain Psyche which would have given me a pretty substantial advantage, so I decided that I would not use it during the fight.
So I got to Trapdoor, popped four small purples and proceeded to attack him. My method was this: use whatever Dual Pistols attacks that weren't recharging. As I expected, he immediately bifurcated. I did a quick scan, found his bifurcation and killed it. Trapdoor followed me so I didn't waste precious seconds tracking him down again. With the small purples I was softcapped, so I could focus on pouring on the damage. I got him to about 50% before he popped his next bifurcation. I'll admit, I got lucky and he spawned right on top of me. I killed it and went back to Trapdoor. At this point my purples had faded so I popped Build Up and hoped I could get him down to 25% before he killed me. Fortunately I did, right as he popped his third bifurcation.
So yeah, armed with little more than my past experience with Trapdoor, without IO sets, without much knowledge of the character I was playing, with DRAIN PSYCHE TIED BEHIND MY BACK, with just four small purples, I beat Trapdoor.