The biggest technical/gameplay problem is precision, I think.
If I understand you correctly, you just want to stop a standard Zelda game every second or so, in which the player can make an input - which is then performed in the next second.
Game freezes if you are not holding any key, if you do press some key game runs for a second. There are two ways to do it, plus variations. One is to NOT make turns last set amount of time, but as long as you are pressing any key, that's what Red Rogue does in its turn based mode. The other way, what I actually proposed, is to make turns last some set amount of time - for example time that would move character exactly one tile, or half a tile maybe. This should work for games that are not using diagonal movement, but for those that do it would possibly require different timing for diagonals so character stays in sync with tile graphics grid.
So, let's say, you stand just outside of reach with your sword, maybe even a bit to the side of it, so you can't just move straight up to it. So you press diagonally on the D-pad. But what do the monsters do? Do they stand there? Do they move in some random direction? Do they start an attack, just the moment after the game pauses? You don't know! You might as well bump into one - which damages you! - as well as being in no better position to attack than before. Swords would probably be utterly useless.
How is that different than turn based roguelike? You seem to describe situation where turns last too long, but if 1 second makes the game too hard we could always make that time shorter.
In any case I'm glad you noticed a game would not necessarily become easier in every way. Imposing turn time intervals with only one action per turn brings some new challenges on its own, makes the game more tactical.
In regular roguelikes, when you bump into a monster you attack them automatically. That has a reason! Zelda is not made to be played turn-by-turn, it's purely designed to be real-time!
I think roguelikes on consoles mostly use action button instead of simple bumping. It adds to immersion, especially together with sound effects. Bumping is not better, just very slightly simpler. But with Zelda controls you could execute different moves, and wouldn't that actually be more fun?
It's not made to be played turn-by-turn doesn't mean it would be any worse than any other turn-based roguelike.
So why don't we just make the intervall shorter? How short? When will it become too tedious? And if we have to drop to an inpt every frame, or maybe even every second or third frame, why don't we just spare ourselves the agony and just play, like it was intended?
How is that any worse than some roguelike? Interval can be adjusted.
I don't know RedRogue, but I'm pretty sure if it can handle both turn-based and realtime gameplay, it was designed that way from the get-go. Zelda just wasn't!
It's just normal real-time game that can pause itself when no key is pressed. You have to try it. Then you will realize the same could be done with any game just the same, and that game can still stay challenging and fun, maybe even more enjoyable if you are into turn-based games already.
P.S.
I finally managed to find some emulator with source code I could actually compile. It's some crappy NES emulator without sound, but it should be enough for gameplay demonstration. I think in a day or two we will be able to actually try out the original Legend of Zelda for NES in this new amazingly fabulous turn based mode. Until then I still welcome all the bets.
I bet 5,000 points it will be pretty cool actually. Place your bets please.
