35 minutes makes me think they're going to announce something new for Switch, whether that's Virtual Console (unlikely), OS features (possible) or some new games (likelihood depends on the game). That would be a long time for them to spend most of it talking about Splatoon 2 and Arms. I mean how long can they realistically spend talking about Splatoon 2? They've shown us quite a few new maps and we've had a chance to play with the dualies in the Test fire. I feel like 10 minutes would be the max they might spend showing off Splatoon 2.
Heck even Arms I can't see them spending much more than 10 - 12 minutes on. That's a long time to be spending talking about one game, especially something like Arms which is a fairly simple looking game from what we've seen so far. Oh and before anyone starts hurling abuse: it looks great fun and seems like it will have a fair amount of nuance in it's control system, weapons and characters etc, but that doesn't stop it being a relatively straightforward premise.
I'm also not sure they will really spend all that long on 3DS stuff. I mean we may see more of Fire Emblem but, again, even 10 minutes would seem like a LONG time to be talking about 3DS stuff.
I mean the Fire Emblem direct was what, 15 minutes? That covered Fire Emblem Heroes, Fire Emblem Warriors, Fire Emblem Switch (albeit with very little info) and Fire Emblem for 3DS. So if they spent 15 minutes talking about 4 games I can't see how they're really going to spend 15 minutes talking about 3DS exclusives.
They say it's a Switch and 3DS direct, but my prediction is the 3DS stuff will be a sizzle reel. Maybe 5 minutes. It would be odd, I think, for them to spend more than 5 minutes on what is essentially a last gen platform, no matter how many people own one. Sony didn't spend hours talking about PS3 games 1 month after PS4 came out. They didn't do any of the "well we better talk about PS3 incase PS4 bombs" stuff which people seem to think Nintendo will.
I just don't buy the whole "3DS is their cash cow and they need to keep talking about it in case Switch bombs" argument. If Switch bombs, Nintendo aren't going to say "bugger it" and go back to churning out all their games on ancient 3DS hardware. They'll release a smaller, lighter, cheaper Switch. Give it up guys, 3DS had a good run but it's coming to an end. They obviously won't say out loud "everyone chuck your 3DS in the bin, show's over", but that's probably what they're thinking internally. If games are still coming out for 3DS it's likely because they were already well into development by the time devs were able to get their hands on Switch dev kits.
If the 35 minute rumours are true, my prediction is 20 minutes on Spla2n and Arms combined, 5 minutes on 3DS stuff and 10 minutes on ????. That ???? could be more details about OS features such as apps, it could be more information about how their online system is going to work, it could be more footage of Fire Emblem Warriors, it could be a total megaton like a Pokemon Stars announcement (fingers crossed but not holding out any hope at all as I suspect this would get it's own Pokemon direct but hey, ORAS was a total throwaway announcement and if Stars is literally just Sun and Moon in HD they may not feel like it's worth making an enormous song and dance about it.)