I'm playing a buffet beach world right now as well!
(Not hardcore though.)
I'm not sure I agree with your suggestions though.
I think that would make it too easy and remove the challenge.
Particularly since you only need to get one grass block and one mycelium since they both spread to dirt blocks.
I was sort of disappointed when the wandering traders turned up in my beach world selling saplings, I was enjoying running around chopping up shipwrecks for the wood. Also when you no longer needed silk touch to collect cobwebs.
Once you have saplings, seeds and animals to breed it doesn't really matter what biome you're in.
Also there are mods and server plugins that add something like what you're suggesting.
Yes of course more options like turn off wadering trader would be more fun but i want from time to time something more.
And the chance of getting dirt should be difficult and on the beach you can get only turtles and lamas from trader if im correct but i was thinking of getting expensive spawner eggs as optional thing. jaust to know how far can i get in hostile place like beach on hardcore something like skyblock.