The thing is, cycling plans on TR aren’t that firmly tied to one another, e.g. you could follow sweet spot base by one of a variety of build programs, depending on where you’re going. The feature you suggest might only make sense to triathletes, and then it wouldn’t save that much time anyway (as others have noted).
Also, you may want to put some air between the 3 plans (or at the end) to account for sickness, holiday breaks, etc. You can always push weeks forward or back, along with the rest of the plan, as you go along. I started the Half Ironman Base 28 weeks before my A race: 24 weeks of scheduled training throughout the three consecutive plans, two week-long skiing trips, one week-long tri camp and an extra week for sickness or unexpected travel, or just in case I wasn’t able to train properly through the May vacation.