Honestly considering we've had Gameboy with Gameboy Advance and DS with 3DS they certainly can.
Going Switch Pro would be a bad move though considering it may lead to misinterpretation with the PS4 Pro comparison as an upgraded Switch(rather than a successor) which is part of what happened to the Wii U.
That being said, I'd say it would be hard to guess the name that will be used because ultimately if Nintendo are adding some sort of new feature to the successor, they'll probably adopt a name connected to that. If it doesn't add other features and is just more powerful then Switch Advance isn't a terrible idea.
Probably would be a good time for them to redesign the joycons a bit though, would make the Switch 2 more physically distinct from the Switch which wouldn't lead to the same confusion.