Not a bad idea at all, but I don’t really want him to be a Sage: there honestly isn’t much of a reason to make him be one when he already has the Triforce of Power. I know Zelda was a sage but I’m retconning that in my headcanon, or at least partially. Lemme explain:
-Apparently, Sages don’t awaken unless there is great danger, so with that bit of information I think it’s safe to assume that once danger passes, the previous Sages are no longer needed and thus are allowed to step away from their role as a sage. So let’s go with that: after the events of OoT, Zelda did indeed step away from her role as the Sage of Time just as the others have.
-In a political sense, the Seven Sages never fully existed, or at least not officially. They operated a lot like a Champion did in that they were chosen warriors that protected Hyrule, the best line of defense, and while they didn’t quite have a political title or power their title as a Sage came with the allowance that their word is significant (and therefore still held weight even in places they technically aren’t a part of). In fact, when The Champions came to be, I’d like to think how the Seven Sages worked was what built the groundwork for its construction.
-Aaaaaaaaaaanyway, given the time having passed without any threat from Demise, new sages aren’t active aside from the Dragon Guardians. Speaking of them, though, they will eventually find successors to take on their role as a Sage, of which I propose a character for their mentorship below.
-If I do end up making them a tangible thing in the current timeline, I’m not…. entirely sure who would be the sages, actually. I have some ideas but nothing too concrete yet, but here are my proposals for them in this timeline anyway:
-Urbosa (Light)
-Medli (Earth) (successor to Saria/Ordona )
-Yunobo (Fire) (successor to Darunia/Eldin)
-Revali (Wind) (Successor to Rauru/Lanayru)
-Mipha (Water)(Successor to Ruto/Faron)
-Midna (Shadow) *SN: I’m combining Shadow and Spirit into one element*
-Paya (Time)
—-
And while we’re on the topic lemme just lay out the groundwork for this timeline’s current Champions:
-Urbosa (champion of the Gerudo)
-Daruk (champion of the Gorons)
-Teba (champion of the Rito)
-Sidon (champion of the Zora)
-Impa (champion of the Hylians)
—–
I got a bit long-winded there but I hope it answers your question/suggestion o3o