I don't think it's an issue that Disney can't do more projects at the same time, I think it's a matter of pacing things out to maximize ROI. I think DCA has been under-built since opening and the surge going on now (Avengers, Coco, Avatar) which could be thought of as DCA 3.0 (or 3.1, 3.2, 3.3 respectively) is playing catchup (it's not healthy to be charging the same ticket price for both parks and the 17 million to 10 million attendance difference sends a message back to the company: that isn't working for guests).
But I don't think it's ideal to be opening new attractions boom-boom-boom 1-2 years apart. I don't think they maximize ROI that way. Each project should have a few years to be the focus of marketing, word-of-mouth and be the star. With boom-boom-boom you step on your own toes. When Coco opens, nobody will be talking about Infinity Defense. When Avatar opens nobody will be talking about Coco. People have short attention spans and focus on "newness."
Once this surge is done, I think there will be a pause on huge projects at DCA for the most part (kind of like the pause on big projects in the 13 years since 2.0). There may be some enhancements and one-off additions, perhaps one or two that are kind of substantial, for example they could put a Fantasyland style dark ride here (queue below, Peter Pan style suspended ride above). There are other tuck-in opportunities scattered here and there.
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But I think Simba will open about 15-17 years after DCA 3.0, just like the current surge is opening 15-17 years after 2.0.
Part of this is looking at DLR holistically and I do think there's a strong possibility of a Tomorowland project in the 2030's. Again, not that they couldn't do projects at DL and DCA at the same time, but for marketing purposes it's better to space big expansions out at least 4 to 5 years (so a new Tomorrowland could open in 2035, say). I actually think there may be two Tomorrowland phases/projects, the first after closing Subs, Autopia, and Monorail (temporarily, for rerouting/shortening) would involve the spaghetti bowl. Then a second would involve core Tomorrowland. That could be 2034 and 2038 for example. Then attention swings back to DCA.
As far as how Simba will get built, you describe an approach starting in early 2030's to mid 2030s to prep for and get bridge done (if I'm understanding you right). I don't think it'll be a stretched out process. When they're ready, I think it will be as tight as they can make it. For example, Disneyland Dr. traffic will be rerouted through the east side of Simba, they'll grade, dig for and form abutments, build bridge, put Disneyland Dr. back together (in say 18 months) and then start on Simba and be done with that in say, 4 years. So 5 to 6 years total, perhaps starting in 2037 or 2038 (around when Tomorrowland concludes) and opening between 2042 to 2044.
This is all just my speculation of how I personanly see things playing out, addressing your initial question. But who knows, Disney is unpredictable!