When Nintendo does a remake, often it isn't simply for the purpose of cashing in on a nostalgic fanbase looking to happily fork over any amount of money on a rethreading of their beloved comfort game. Time and time again throughout the Switch and Wii U generation, we see this story repeat itself: [1.] Ocarina 3D & Wind Waker inspired Breath of the Wild, [2.] Link's Awakening remake equipped Grezzo with the engine and expertise to develop their own 2D Zelda (Echoes of Wisdom), [3.] Metroid Samus Returns marked the return of 2D Samus and would be followed up wtih Metroid Dread only a few years later, [4.] Metroid Prime Remastered preceded Metroid Prime 4: Beyond (a game with an infamous development timeline, likely incorporating Prime Remastered so as to help the newly formed team at Retro learn what makes Metroid Prime what it is), [5.] Famicon Detective Club remakes and the creation of Emio, and so forth.

That said: Here we have two remakes— Star Fox and The Legend of Zelda: Ocarina of Time. The former already has strong rumors pointing toward a brand new, original mainline entry (see this Reddit thread for a brief recap of some rumors), whereas the latter we know nothing of future developments for

(i) Do we think this remake will lead to a resurgence of traditional 3D Zelda alongside the open air formula?

(ii) Is it possible the mainline Zelda Team is remaking Ocarina so as to relearn what it means to make a "Zelda dungeon" for the next mainline open air Zelda, following lukewarm reception on the dungeons of BotW/TotK? Could we see a Majora's Mask remake using the same engine? (Please, Nintendo!! I will give you anything for a Majora remake in a similar manner to that of Ocarina!)

...Or am I looking too far into this, and the Oca-Remake is nothing more than Nintendo needing a game to launch alongside their big Zelda movie? Share!

Majoras Mask remake seems the most likely. After all MM re-used a lot of assets from Ocarina so the remake of Majoras can do the same.

I don't expect Ocarina to sell as well as the openworld Zelda's so I think new mainline titles will stick to the BOTW/TOTK formula.

I also feel like a Majora's Mask remake is the most likely. I could see it being released five years after OOT remake (2031). We'll probably get a new Zelda around 2029, so this gives them all some breathing room. Would be cool if the next new Zelda has better dungeons in an open air setting, but I don't see OOT remake being what changes that.

I think (and have thought for years) that the next 3D Zelda will still be open world but perhaps shrunk down a little, more traditional dungeons and progression, and Link's green tunic will be the main outfit again.
A blend of the Wild duology and the previous 3D Zeldas while having new stuff too.

Hopefully, they will combine the two and make next Zelda what it was supposed to be - item gated open world with proper dungeons, like original LoZ was.

I think a Majora remake is pretty much a given at this point, as much of the legwork for it is now done.

Personally, I can't see Nintendo abandoning the open air format as BOTW is still by far the best selling Zelda ever, though I can see them incorporating more classic elements like how TOTK already brought back themed temples.

You are overthinking this.

But yes, a new Zelda game is most certainly in the cooking. What I personally would like to see is a ”new” take on the franchise like AoL was and I would argue BotW was (after decades of linear point A to B games).

Bold: Not suggesting that Nintendo would abandon the open air formula, but rather do as they have with series such as DK (2D v 3D), Metroid (2D v 3D), Mario RPG (Paper v M&L), and so forth. That is to say, a 3D traditional subseries alongside a 3D open air subseries for Zelda. Sorry if that wasnt clear.

They will learn that BotW style games sell better than Ocarina style.

Whatever I actually want and hope for Zelda, this is most likely outcome - BotW had enormous influx of first time players, some of them stayed for TotK, some of them even then played and liked older titles. But I think for the most part, Nintendo can't go back. 

What they can do is try to combine open world with item gated progression, like Zelda 1, but they would need to scrap a lot of things in how items work from BotW formula for that and use original approach - now, would Anouma's hubris allow for that is another question.