You can get tubeless tyres for racing bikes, well there's two of them! Apparently the tubeless road tyres can be run at a slightly lower pressure for increased comfort without sacrificing efficiency. Most roadies spending £500+ on wheels want them the wheels to be as efficient as possible; so they wont like the idea of running the tyres at a low pressure. Which is probably why tubeless road tyres have never caught on.
I've yet to see a tubeless slick MTB tyre so you'd have to use a normal tyre and some sort of sealant (Assuming this works). I doubt very much if running them tubeless would help increase grip on tarmac. I suspect the best you could hope for would be reduced weight and a slightly more comfortable ride.
