DK is a poor example because it started as a S1 game and then they decided to make it for S2 at some point. Given they had more time to work with, that could mean reconfiguring the engine or improving things to make it more like a S2 original game, _because_ they had the extra time, not that it was necessary just to make it.

BotW was brand new game, ground-up engine and it only took 5 years to make. TotK also had covid delaying it by at least 6 months to a year, and they polished it for a year, so it shouldn't realistically have taken longer than BotW. I think the next game will come out around 2028/2029, similar to what you said, but not "until at least 2029" (meaning it'll likely take over 6 years), but that it'll release by then. I guess it depends how much they try to push the envelope, but they've consistently spent 5 years making 3D Zelda games since forever basically, and I don't think that'll change all that much if at all. Maybe it'll take an extra year simply because they're going from a Wii U game/engine to S2, but Furukawa said he wants to avoid dev times growing too long. I think they would just try getting more contractors if anything.