I doubt Emery plays with anything but a trivote as his primary formation. That looks to be Xhaka-Torreira-Ramsey to me, with Mkhitaryan/Auba and Özil ahead of them. I agree he’d probably like a traditional touchline hugger as you say but he doesn’t have that, closest thing he has is Bellerín hence why I think he’ll look to play with a trivote, or occasionally an auxiliary RB/LB to cover–he’s shown he’s not averse to playing with a ‘cuartote’ even at PSG. Wouldn’t be surprised to see someone like Maitland-Niles shunted out to that type of position ahead of Kolasinac/Monreal (my god, we really need a LB) in away games at some point.
We might see him experiment a few times with a 4-2-3-1 against lesser opponents at home, so Xhaka/Torreira-Ramsey Auba-Özil-Mkhi Lacazette, as managers who are coming in trying to comply with an attacking football mandate will try to do in the early stages, but I expect he’ll quickly revert to playing in a 4-3-3 even in those games after not feeling comfortable with the results with a pivot like that, and experiment more with perhaps 5 at the back or options like a Maitland-Niles on the wing as mentioned above in tough away games.
Really don’t think Ramsey is going anywhere, tbh. Him getting injured and the resulting options is scary, though…we’re the typical Ramsey muscular injury away from playing with a Xhaka-Torreira-Elneny/Guendozzi trivote. Can’t really see him going the other way and preferring someone like Iwobi or an extremely offensive formation like Xhaka-Torreira Auba-Özil-Mkhi Lacazette.
Edit: anyways, Emery is clearly not adverse to analytics, so between the fact that it’s impossible not to realize Ramsey’s value if you are not adverse to analytics + him being the only way he can really compose a decent trivote, I would be extremely surprised if he is not central to his plans.