If they were to do a "Switch Pro" with better specs, the way they could get around the issue of splintered userbase is to do this
No. that ain't gonna happen. There is no reason for Nintendo to try to confuse the market. A pro version of the Switch I'm sure would have better specs but not by like double, and not to make it so you could only play games when the OG Switch is plugged in. That sounds horrendous. A pro Switch should just deliver a premium experience, which means games that run slow don't run slow anymore, or games that would run at say 720p or 900p docked get to run in 1080p docked instead. Something like that.
I think a premium experience of the Switch would be:
More performance to make games run smoother or higher res (no splintering userbase)
Larger screen the eliminates the dead space in the current model
More disk space
more scratch resistant screen, maybe better kickstand
bluetooth so you can use wireless headphones
The above things seem like something that would be worth coming out with a premium version of the Switch for $50 more than OG Switch, and maybe even eventually eliminating the original, like 3DS did, so that Nintendo keeps the higher price point into the future, and the Lite remains the low price point, so people who want to "Switch" have to get the most expensive but better (than the original) version. Even if off the bat this new version made less profit than the original, they could market it as a better Switch as so keep the price high for longer and therefore make more profit long term.