If Nintendo waits a long time for a Switch successor, what do you think will happen?

[Wman1996]

Norion said:

What would happen is Nintendo would see a massive decline in revenue from hardware and software sales falling drastically. By the end of 2024 the Switch's momentum will be slowing rapidly so 2026 would be an abysmal business decision.

Given what we know for now, it seems like a bad decision. If Nintendo doesn't release a late-stage Pro and have at least 1-2 more heavyhitters, the Switch would likely be down to 5-7 million a year by 2026 when a successor would launch. And considering how successful Switch has been, that's lower than Nintendo would want.

I didn't mention some of the other circumstances of the Game Boy in the OP. Nintendo didn't plan to ride out the Game Boy until 1998 with the Color and 2001 with the Advance. Those were a result of circumstance, namely that a Game Boy successor with similar specs to the GBA was shelved in the mid-90s due to cost. Virtual Boy launched and died from 1995-1996. If it succeeded, it probably would've leeched some resources away from the Game Boy, even if it wasn't a successor like the DS was to the GBA (despite initially being called a "third pillar"). And of course, Pokemon gave new wind to the rapidly aging Game Boy. Enough to keep it afloat a little longer and come out with the Color. And lastly, there were multiple home consoles alongside the Game Boy during its life. 

The Switch has none of the circumstances I mentioned above.