I'm not 100% but I'm 99% sure they announced Mac Pro would have Catalina which usually means it will ship with it pre-installed.
https://www.apple.com/mac-pro/specs/ and scroll down to 'Operating System' - specifically states Mojave. Not saying that precludes it launching with Catalina - but they certainly haven't committed to that. I don't think it would be acceptable for a pro machine to not at least support Mojave - especially since Catalina is going to come with a mass cull of 32 bit abandonware which users will have to find alternatives to.