I don't think I like any of these ideas, or the idea of them remaking any of the songs. I enjoyed all the remakes they did do while they were together, but I really don't think any of their songs are crying out to be rerecorded or changed in any way. I feel like they never released anything without it being perfectly complete in its own way.
Even the demos are better off as demos than as Hi-Fi, rewritten, sang by someone else, remakes. I think everything that they remade with Gackt, like Ma Cherie, was better with Tetsu even though it's alright with Gackt too.
I don't feel like Közi put things through a Malice Mizer "filter". His songs like Color Me Blood Red and ILLUMINATI are pretty similar to what he's doing with his solo career, and things like Gekka and Ju te veux (well, and ILLUMINATI too) have that circus-y, twisted vibe that's very much like him. I think Malice Mizer was more of a venue for him to experiment with broader themes sometimes rather that as a filter than inhibited him. Songs like Chikasui miyaku no meiro are not his normal style at all, but it's still a song that I feel only he could have made and you can sense that he really was passionate about writing it--it's not like he was forced into making something he didn't want to. It was more like he had a chance to do something new for him.
I think Moi dix Mois has had less consistent recording and composition quality, so I like to see Moi dix Mois' older songs get tweaked a bit and I'd like to see Beyond the Gate basically get completely rerecorded XD. But Malice Mizer is perfectly fine how it is IMO.