Nintendo

Can they keep with the same new formula?

Yes, absolutely.

Should they?

I'm on the fence about this. On the one hand, it's a great formula, and many current Zelda fans have grown up with and have known little else (except maybe Skyward Sword HD). Nintendo has had great success with it, so I can't imagine they'd depart from it soon, as much as attempting to predict Nintendo is a futile endeavour. On the other, I have my gripes with it, and I dearly miss the classic formula.

I think at the very least, they're going to turn this into a trilogy within the same Hyrule. I don't know if it's my imagination, but the oceans and Eventide Island seemed a lot more fleshed out this time around, so maybe they'll do a Wind Waker type thing to be a counterpart like BotW is to Zelda 1 and TotK is to OoT/MM.

Based on some of the BotW concept art, it's clear the team is capable of coming up with a lot of ideas. The "Modern" Zelda concept almost certainly inspired the Master Cycle DLC, and the "Hyrule Invasion" concept potentially also inspired the Zonai stuff. So I think they'll come up with neat stuff regardless.

(Edit for Typos.)

I'd like to see a version of Viscera Cleanup Detail game but a pre-mission where you navigate a perilous dungeon from all the Zelda timeline games, setting up all the traps and puzzles before Link comes by to complete it (hoping you don't fall victim to the traps you are setting up), as well as a post-mission version where you are cleaning up all the gore and dismembered body parts and pottery shards and misc etc that Link has haphazardly hacked-off with his sword or left behind on his adventures through the dungeons.

I'd like to see a tighter Zelda/Link fusion, where Zelda's time powers are weaved more into Links combat.

A hard game where Link dies and dies and dies, but Zelda keeps rewinding time and bringing him back to life, where he learns from his mistakes (similar to PoP:SoT).

As the game progresses and the combat gets harder, Link gains the ability to slow down time in order to better plan his attacks as they happen. He's not moving super fast like the Flash when time is slowed, for he is slowed down too, but he can simply react better; dodge a sword by anticipation, plan a jump off an enemy's head with better timing, turn a dodge under a weapon into an attack in the same stride, all the while preserving his momentum.

By the end of the game, he can literally stop time, and he does so endlessly at the game credits, as its the only way to free Zelda from her time prison. Zelda and Link effectively switch places, and the next game is Zelda trying to free Link

Multiplayer shrines, spin-off game.

In the aftermath of TotK, the world is in a sorry state. The sky islands are falling, violent quakes closed the access to the depths, and embers of darkness (fragments of the secret stone last held by Ganondorf) have fallen to the land and created fields of distortion where the present world has been over written by a section of the past. The worst are the dungeons, where the fragments empower new boss monsters.

Link and Zelda team up together to restore Hyrule with the new gameplay gimmick being the ability to swap between them. Link as a swordsman and Zelda with time powers (some inspiration from Bioshock infinite’s Elizabeth).

They'll make a movie

I hope the success of BotW and TotK doesn't mean we'll never get another traditional Zelda game.

I'm in the camp of people who love the traditional Zelda formula, and I was sorely disappointed with BotW to the point that I lost all interest in TotK and will probably not buy another zelda game if they continue the new formula.

Perhaps Nintendo could incorporate both formulas in some way, or maybe alternate between traditional Zelda and new Zelda games in the future?