I have a pt-ep12 with a Zen WA-100 on it. I used to own the epl2 & housing and had used the WA-100 there. The port interface is the same.
The port for the ep12 is a bit useless for me also, but it does accommodate a few other lens. I tried the 17 f2.8 pancake and it worked. Not sure I'd really want that underwater, but it works.
The great thing about the WA-100 to me is that I can also use the 60mm behind it. So, with that one port, you can use the 14-42, 9-18 & 60.
I recommend putting the WA-100 on the ep12 so then you can use your full range of lens with the better camera.
Leave the epl1 as is. You can still use all those same 3 lens on behind the standard port. Biggest difference is you don't get the full wide angle of the dome.
Of course, you sacrifice some magnification when using the 60 behind the WA-100 semi dome, but it really has not been an issue for me.
The pay off in flexibility is more than worth it.
And the zoom gears are the same. Same gear works on the 9-18 & 14-42 and will work with either housing.