I know there is that cause I followed switch hacking since before being possible to hack and my switch stayed in the closet many time waiting for the hack from the "girl" that released Fusee and despite I never tried atmosphere on my own switch yet cause I don't use it, I followed all the progress of android, linux, dual boot, custom paylods from SX OS or hekate or whatever, transferring SX OS emunand to atmosphere and all of that...
I also customized my joy-con with a on/off switch and did the same to this friend all free-of-charge...
But I'm almost sure my friend will want a single OS, autoboot straight into it and just want it updated to install all the latest stuff and run anything in it and leave it indefinitely ON while docked, but he is definitely pissed for not having the USB game loading and no XCI mounting on atmosphere or else he would probably be pissing me off daily to install atmosphere on his switch
I'm sure he could totally use dual boot fine since he even went further than me testing all sorts of stuff on SXOS including emulators which I never bothered my self, but I'm still sure he will want just one OS that he sends the payload and boots straight into it and have all his progress on a single place.
EDIT: Also just the fact that I told him he will probably have to reinstall most or all games again on atmosphere already made him pissed off LOL

(I will probably eventually do him a full clean install with atmosphere emunand some day and not even convert his current one, FRESH START like he knows that's the best and true only option on windows computers

)