Sounds like what we need is a system of "tubular tubeless" so sealant can work effectively.
To add to what my candadian brother said, this tech existed already a few years before tubeless tyres. I'd even go as far and say it actually gave birth to tubeless tyres.
First brought to market by Tufo, the company that invented it (I think), it consisted of producing a tubeless tyre casing that was rendered airtight by a process that allowed to deposit butyl to a rubber casing.
IOW instead of having a separate inner tube and casing they actually developped a process which allowed the casing and inner tube to act as one and not leak air.
Except that they made a few mistakes when trying to market it: Tufo used materials that were questionable at best. Rolling resistance was sky high to be polite.
Schwalbe, a company belonging to the same group adopted the design and offered its own version with the same lack of success.
Once you know that either companies are more of investment groups rather than true tyre makers still not capable of manufacturing a supreme tyre to this day despite all marketing efforts you may start accepting that what, in principle, sounds like a good idea, is not automatically a key to success.
Later on Continental, not wanting to be left behind technically, produced similar tyres with, once again, the same lack of success.
The main resaon for this, to my mind at least, is twofold. A tyre like that is best build around a supple casing, not your typical german tank casing. The other reason is that once such a tyre is shot by a puncture that no sealant can cure there is just no way of repairing it.
You just have no other choice but to throw it in the bin. Not really appealing to the buying public.
Still, what stopped it dead in its tracks was that it was a product targeted at the wrong public, namely the regular tubular user who was not waiting for yet another mediocre tubular, and the decision makers of the races or even the tubular afficionado who were expecting superior performance and were disappointed. So none of them saw any improvement in performance (due to the lack of flex in the casing mostly I suppose) you'd expect to see.
Enter, tubeless tyres which, AFAIK, for road use has turned out unsatisfactorliy too. For similar reasons and other politico-industrial ones as well.
All in all not such a bad idea technically speaking. (B)Right idea at a bad time, I guess....