Nintendo

Depends on how much of a departure the successor is from the original Switch. If it's a completely different machine, it needs a completely different name. One of the problems they had with the marketing of the Wii U: it was a totally different console from the Wii, but branding it with the Wii name didn't convey that well enough. The Game Boy line worked up to the GBA because each new iteration did basically the same things as the one before it, but with improved internal hardware. The DS changed things up enough that a new name was warranted. If the successor to the Switch is basically/mostly an internal hardware upgrade and they stick with the handheld/dock mechanic, keeping the Switch name makes sense from a branding and marketing standpoint: the Switch sold like hotcakes, this is a better Switch, capitalize on that. But if it's straight up its own thing, tell people that with its own unique name.