Seeing as how the Switch is a portable system and the PS5 isn't, I don't see the PS5 copies having a huge impact on the price of Switch copies. If people just wanted to play the game on any console and didn't want to pay $500+ for a switch copy, they most likely would have either bought the PS4 physical version (Still pricey, but not $500+ pricey) or a digital copy on the numerous platforms. Much like how some people thought that the Shantae re-release on GBC by LRG would impact prices of the original GBC release (It didn't), I can see why people would think the same with Pirate's Curse, but it won't.
For one thing, plenty of people simply won't purchase the PS5 version because they can't get their hands on a PS5 yet, and are probably thinking that they'll just pay x2 as much on the second hand market when they can finally get their hands on a PS5. I've always found the logic of "I won't buy the games until I own the console" to be stupid, since you run the risk of missing out on awesome sales on games that you know you'll want to play later on, but that's how many people operate.
Oh, and the Switch is a Nintendo console. I mean, do we really even need to go over the fact that Nintendo ports of most games seem to always cost more than on other consoles? Plus you've got insane full set collectors, and Shantae collectors as a sub group, and bla bla bla. The only thing that's going to impact the switch port of Pirate's Curse prices, is the overall softening of the market right now.