I don't think you're going to find one solution that's perfect for both long-distance and TT/Ironman. I do a lot of long-distance, and everyone I know, including several RAAM finishers, just attaches clip-on's to their race bike. Something like that DRV/AEROa (or any handlebar with a 31.8 diameter attachment point) and a Supersonic Ergo 35c would work well for the 12/24 hour races. You won't need a low-rise stem or integrated handlebar hydration for those races.
https://www.bikeforums.net/long-dist...endurance.html
I also have several ironman friends who all have triathlon bikes and tell me it makes a big difference in speed and something about the geometry saves their legs for the run. It's only about 6 hours on the bike so comfort isn't as important as an ultra-distance race. I was only kind of paying attention since I have no interest in ever attempting an Ironman myself. I don't know anyone who does both ultra-distance and Ironman in the same season. They both require a lot of training to be fast and it's not the same. Check out the GLR schedule if you want to try some long rides with us next season. We have a few super-fast guys.