The good news is, the retroarch has been revamped in this image a lot to allow it to be used almost exclusively. That’s the positive. With this come a slightly longer load up time, and potentially laggier interface. That’s part of the reason people may opt to use the standalones.
I would very much love it if you could test things out for bugs! In fact, I have a copy that has all of the stuff from that previous post applied I can whip up straight away, if you’re keen to just test things out right away. Let me know! (please!!)
Re: Sigil.wad, Surprise! The chocoDM in the launcher should run it, as long as you put it in the /home/cpi/games/chocoDM directory. It should appear in the list.
Otherwise, if you’re really into doom (judging by your avatar haha) check out this post that @Lix made, re: installing zdoom. You don’t need to necessarily use it with brutal doom. It’s a solid custom wrapper that runs a whole heap of things. I’m almost tempted to include it with this custom image, as a replacement for the chocoDM wrappers. Let's play Brutal Doom!