I'm curious, if they say they're revealing it next month then does that mean it's something that will be releasing this year? If they're gonna reveal something that's coming in 2019 why not just show it at the direct instead of a month later, that E3 direct already had a couple 2019 games in there anyway. But then again the Wolfenstein 2 port was revealed back in 2017 to be releasing in 2018 so maybe not. 

Anyways, in terms of "major" maybe GTA V, Fallout something, Kingdom Hearts 3? I dunno.

If they really showing it next month, its probably this years game, Nintendo tend to announce 3rd party ports only few months before launch, last year they announced Doom in September Direct (not at E3) and released it less than 2 months later, I think they announced Wolfenstein 2 despite it was 2018. game in same Direct because of "announcement of package of two shooters from Bethesda".

Octopath Traveler?

Thats not port, its brand new game and actually Switch reveal announcement.

I can only hope so.

Please

Please

Please

Im guessing Fallout 4 or 3? Both were heavily rumoured and I think GTA V is gonna be announced at an E3 (If it ever gets announced which Im also doubting. 

After reading the comments I have to make an honest question: Why are some of you naming newly announced games like Fallout 76, the new Quake and Wolfenstein or even REmake2? Those games wouldn't be in development alongside the other versions of those games, so it wouldn't be a port but a version of it. I mean, I don't see anyone saying that the PS4 versions of those games are ports, right?

Because of that, I think that this game is a port of an already released game. Which one? I have no idea.

No idea. I was hoping for Nier Automata, but it seems that, while Platinum would like that to happen, there's not Switch version underway yet.

Maybe it's Fallout 3 or 4?

Something from Bethesda ... Fallout most likely, or Prey. I wouldn't be surprised to see Elder Scrolls Online too.