I am not stating in the installer that they have to vanilla. However, I am adding an extra page to the installer which deals with compatibility.
That page states that MEHEM is self contained and can be compatible with other mods, according to their documentation.
I also include a ink to a MEHEM + texture guide (dummy thread already exists in ME3Explorer forum), which will have detailed instructions for that. In this guide, I will tell people to vanilla their game completely, then extract all their DLCs manually, then redo the treescan. That's the only way it works for me and it's a really complicated process at the moment. The only reason the guide is not finished yet is because I am still testing what actually works. Frankly, DLC extraction, whether done with the Texplorer tree scan or with DLC Editor 2 is a mess and I need to find a reliable way how that works (so far, just the proper DLC extraction has about 25-30 steps!!!! This si ridiculous and I am trying to actually improve on that.).
In short, I am not requiring people to vanilla their game but I only tested MEHEM on a vanilla game and that's all I am going to provide support for (that and the texture issue, which will require people to vanilla anyway)
If people want to try and combine MEHEM with other mods or if they want to try and install it without vanilla-ing their game first, that's up to them basically because given the variety of mods that exists these days and the way people may have messed u their games, I can't test it all.
Edit: As for appending new DLC mods to the texture tree: It would be nice but the first priority is to get it to work even from a vanilla game at all (right now, it doesn't). That should be feasible, all we need to do is get that automatic extraction to work properly.
I am also not sure how interested KFreon is in this issue. Could be fairly tricky to get this to work without introducing a huge amount of bugs into the treescan procedure.