Ok guys, the original poster specifically asked about the 8mm FE on a PEN housing with precision dome.
Now, let's compare the size weight of a PEN housing with the precision dome and what ever RX100 housing you chose with the necessary add on lens to get you to equivalent FE view. I don't have those numbers, but based on my experience with the Inon 165AD I'd be willing to bet there's barely a scintilla of difference in size & weight.
And what about the optical performance of the compact camera lens and then going through a flat port, then an add on lens.
As opposed to a dedicated FE lens and port. That's what he asked about.
I gave my EXPERIENCE with the ZEN semi dome which works well for some of other lens.
It would be nice if someone gave actual experience of the precision dome with the 8mm on the PEN housing.
Interceptor in your list of weights, what is the weight with an add on FE lens?