Even assuming a major spec revision is in the cards, a hypothetical "Switch Pro" is still a Switch, and will highly likely be treated like most other hardware revision by the market. The New 3DS and DSi did improve sales, but only temporarily. The market responded to them like they would a price cut, and a late-life price cut at that:
The short-term gains are obvious, but after that initial boost sales quickly dropped back down to the previous baseline or lower over the course of 2-3 months or thereabouts.
We saw much the same with the PS4 Pro and Xbox One X, the first major spec revisions for a home console since the Japan-only SuperGrafx (an upgraded TG-16/PC Engine). The Pro had a minimal effect on PS4 sales, while the X1X gave a modest multi-month boost to XBO sales (at least in the U.S.).
The only time a spec revision resulted in a huge boost in sales was the Game Boy Color. While it was short-lived, it posted remarkable sales. While Nintendo never gave specifics as they never separated GBC sales from sales of older models, both NPD and Famitsu data indicate a substantial portion of Game Boy sales were from the Color. In the U.S., the GBC's share of total GB sales was at least 40% (while there's no official NPD tally for GB sales in just the U.S., based on the U.S.'s average share of Nintendo sales in "the Americas" region, it likely sold on the order of 38-39M units; NPD numbers show about 17.3M Colors sold). In Japan, the GBC's share of GB sales was a much more modest 17.5%, but it was still healthy numbers.
But the GBC had the distinction of releasing nearly a decade after the original model Game Boy did. It probably also helped that it A) had a rather high amount of exclusive games that did not work on older Game Boy models, B) was released right around the same time as Pokemon, and C) was in freakin' color. These factors resulted in gamers, especially in North America, treating it as a new console entirely even though it was technically just an upgraded Game Boy.
If we get a "Switch Pro" within the next year or two, I expect the reaction to it will be more like that of the DSi or New 3DS, being treated as simply another model like the Lite. It will give a solid but relatively short-term boost to sales, but will not serve to reverse the inevitable terminal decline in Switch sales. Eventually, everybody that wants a Switch will get one, and only those that want a slightly better model will get that one. The Switch's "true" successor will probably be a completely new platform, a clean break from the Switch. I think it may stand a good chance of being another hybrid, and if it is, it will be a true next-gen experience and not a mere spec upgrade.