People generally dont expect Musk to go to the ISS on Crew Dragon - because he's not an astronaut. But if SpaceX start doing 'space tourism' aimed at general (if somewhat rich) consumers then it would be odd for Musk not to take a ride on that - dont you think?
Similarly Branson would be expected to have a go on his space tourism thing once it opens up to the public.
There is no "if". SpaceX has planned missions and contracts for many more.
That's someone subcontracting, a bit different to Blue Origin and Virgin Galactic saying "buy a ticket here"
Musk was known to joke that the (pressurised) Cargo Dragon spacecraft had everything needed for a stowaway to visit the ISS. Thank goodness he didn't try it - probably a stunt too far even for him.