Formula, I'm not sure what sort of changes you want to see. Like, big sweeping changes to the gameplay style? I don't know if that would work, let alone if Nintendo would allow it.

Look to their other franchises: Mario (aside from his non-canon sports/party games) has only seen superficial changes over the years, from completing levels to achieving goals within levels (collecting stars). There was the example of Super Mario Sunshine, which generally felt different from the other Mario games to the point where, while it was enjoyable because it was Nintendo-polished, you could have plugged in a whole new character and called it something else.

Star Fox has flown in his arwing in all of his games, although Star Fox Adventures saw him venture outside for the longest period of time, enough so to call it an entirely different style of game. If anything, the shooting sequences felt tacked-on. The game was still fun, but again, not StarFox-fun. It's no surprise that Rare was developing it as something entirely different before Miyamoto bogarded the project and effectively pissed Rare off enough to leave for Microsoft.

Making a Zelda game where Link does completely different things from the original gameplay subset of adventuring through dungeons with a sword and shield would be purposefully creating a black sheep of the franchise, like these other two games. Both were still successful, but in the memories of gamers, neither are likely to be the favorites. And we're still talking about a franchise with both AoL and MM, solid games in the series but not like their counterparts.

I can play through Zelda games over and over, knowing full well where things are and still enjoying the amount of freedom to what the game wants me to do. They expanded gameplay significantly over the years with the addition of heart pieces, fishing, instrument-playing (instruments were always there but starting on the N64 you could PLAY them), mask collecting, and sailing to name a few.

I don't want a Zelda RTS or RPG (unless they surprise me with SMRPG-style quality), but I know some do. I just don't feel like it would fit in with the other games. What do you think?

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My timeline theory:
Same sword, different day.