GenesisPlusDC supports the following extensions: ".zip", ".gen", and ".bin".
I posed the very same question about gens4all over at the Dremcast.es forums, but haven't gotten a response. I think the prevailing view is, it'll happen if it'll happen. Right now as far as I know gens4all is still being worked on until I'm told otherwise, and genplusdc had reportedly been resumed by some of the dc veteran coders.
A couple things I know are that the sound will never be perfect, because of the dreamcast's hardware limitations. And these guys have personal/social lifes, so we may never see an update...
GensDC supports .bin, .gen, .smd, .zip, .gz and .7z. I think it is more than enough. It features a customised, cursor based menu.
And i have been losing my personal/social life for a while so yes, we will have an update, but heh, you want an update or you want anything along the same lines it used to be?
As a progress report, i have been dealing with some nasty issues, most of which are gone by now. Unfortunately, it is taking longer than i wanted, but that is the way it is. Basically, there is still work on the VDP and the sound emulation. The speed improvements on the VDP are really promising and worth waiting for. I will not get into numbers, which usually create a lot of confusion.
As soon as i have something i feel happy with, i will provide a beta to Chris and next will be the first beta release...