Don't own a Switch yet and all these rumours about a more powerful one drive me crazy. Have no idea if I should wait past black friday or not
Nintendo software and hardware generally retain a lot of their value so if, and that's a big IF, Nintendo launch a Switch Pro in a year or two you will easily be able to sell or trade your Switch in and pay a small amount to upgrade.
You may end up losing $100 or so but then you will have had over a year to play the Switch in that time. Hanging on forever doesn't make much sense unless you're especially broke.