I'm a bit torn on the idea of an ultimate iron man mode (I'll refer to it as UIM). On the one hand it is always exciting to introduce a new way to play and to spark up some competition between players who like to compete for the top spot on the highscores.
However, I can see it having a similar fate to the Ironman mode we currently have. In the beginning it was extremely popular, it seemed like everyone wanted to try it out. However, we now have very few active ironmen ingame and it's been the same names on the front page of the highscores forever now.
It was the competition that made it extremely fun for me, but now that very few people are pushing for the top spots I lost some of the interest that I had in the beginning. UIM would reach the same fate but much quicker.
I believe that an UIM would not be as popular as you might think. Only a handful of players have shown any interest in it at all, which begs the question is it worth the time to code and implement, if no one is going to make use of it?