In practise it's actually 3GB vs 5GB/5.5GB (the X1 and PS4 reserve a lot for the OS, apps, background functions like recording, etc), but the bigger problem is speed. The Switch's RAM is really slow, at least compared to none portable devices. It's bandwidth tops out at 25.6GB/s, compared to 68GB/s for the X1 (+32MB of high speed eSRAM), and 176GB/s for the PS4. That's obviously a pretty big problem for a game that wants to constantly pull in and out large amounts of assets.

That said, I'd be shocked if it's not possible. I expect it's more of matter of "can we do this at a level in line with our quality standards, and without too much fuss" rather than "is this possible?". Hopefully they can, while I don't play any multi-plats on the Switch, it's always really cool seeing how games come together on it. It's a testament to how far mobile tech has come that some of them are even possible.

I say, don't push it.
You can release the first game, though.

give to panic button, let them attempt

Wolfenstein?

Not id made but using id Tech 6.

Panic Button senpai,help us!

Hah, I see that game was given to Machinegames to develop. But the IP is from id, Wolfenstein 3D even precedes Doom as an id game (and is often dubbed the first First Person Shooter). So factually is Wolfenstein no id title, but the IP originates there, probably they still have much influence over the series.

I'm surprised they're looking into bringing Rage 2 over as opposed the Fallout 4 which would be easier either way it's positive from Bethesda I think the ID engines must have a positive response from the hardware, I find it bizarre that of all the western developers they're the biggest supporters of the Switch.

Zekkyou basically said what I would have posted.  Bandwidth is going to be the big issue.  If the game has to freeze or lag when you get to transition points then that would be a major problem.  Asset reduction would help but I have no idea if it would be enough.  However, if they're looking into it, then I think that indicates that they think it's in the realm of possibility.  If they didn't, they probably wouldn't spend time and money running tests.

I very much doubt Fallout 4 would be easier.  It's an old engine that already struggles under the new systems they've integrated into it, plus all the object tracking it handles.  It would probably take a serious amount of work and time and even then the performance might be abysmal.  That's a different situation.  

Of course they can , but with what sacrifice?

Even Doom 2016 that is corridor shooter already run below 640 p with frames rates between 20 to 30 FPS and not include ultra downgraded graphic.