I have owned a Nomad for over 10 years and still use it as my primary sidemount rig despite having several others and helped design several more. I have used it with doubles as well.
With doubles, it struggles for the vast majority of people, especially if you are diving a drysuit. The wing is designed to have maximum lift at the bottom of the wing to deal with the natural tendency in sidemount to be foot heavy which is counter to the trend in doubles where you want the lift up high since the tendency is to be head-heavy. It also won't accept a stainless backplate, so you are going to struggle on where/how to get lead on the rig if you are diving in cold water.
In sidemount, for most people the rig is physically too long/wide. If you are not over 6ft then you shouldn't be looking at the Nomad XT, and if you are really skinny, you shouldn't be looking at it either. It requires significant modifications to get it to behave properly
The SMS100 is the other one that will do it, and it is even worse, especially at doubles, but needs even more significant modifications to get it to behave in sidemount.
My advice is just get a used SS backplate and doubles wing. You'll be far better off for it with a pair of rigs.