What do you think, what is the chance that Port Royale 4 will also appear here?
Kalpyso also has many games at GOG, so the chance should be greater.

I'm pretty sure it will appear here...just give it a few years. :)

I don't think, it will be a day one release.
With a game so big, GOG would do themselves a disservice by not announcing it already as "coming soon", the release is set to September, after all.

But then again - it's GOG, so...

I hope that Port Royale 4 does not do the same as Port Royale 3.
Port Royal 3 has not yet been published on GOG.

Does anyone know if Port Royale 3 also has the Kalypso Launcher and if Port Royale 4 will also have the launcher?

Wishlist
https://www.gog.com/wishlist/games/port_royale_4
https://www.gog.com/wishlist/games/port_royale_4_standard_edition
https://www.gog.com/wishlist/games/port_royale_4_extended_edition

Does it have battles, or is it just trade?

There are also turn-based naval battles

I play Port Royale 3 on Steam. There's no Kalypso Launcher.

BTW, Rise of Venice is also not on GOG (yet). You can consider it Port Royale 3.5. Rise of Venice uses Kalypso Launcher though.

I will stick to the first game until it has been surpassed.