Tubless Tubular

Tufo tubs are essentially this (tubeless tubs) - they have a butyl lining to the inner surface of the tub instead of a tube.  They are however IMHO stiff and heavy compared to other tubulars.  You use Tufo Extreme sealant to repair punctures, indeed this is the only way to repair them.  I only have one and it was on for less than 30 minutes before it punctured so I am not convinced it's worth repairing!

I've had mixed results trying to repair tubs with sealant.  Vittoria Pit Stop didn't get me out of trouble when I needed it on the road up to Caerphilly and the Bontrager sealant I added to some Conti tubs seemed to have dried up before it was actually called on.  They guy I sent my tubs to for repair didn't complain about it though.

I find in clinchers that latex tubes are much more puncture resistant than butyl so I'm going to try some latex tubed Vittoria Corsa G+ tubs next but nuzzle me they are not cheap.

Comparing to a tubeless system, apart from slight weight saving, irrelevant to most of amateur  cyclists, this hybrid system would only have disadvantages; higher rolling resistance and inability to fit an inner tube quickly in cases when sealant can't seal larger holes.

I vaguely remember  back in the old eastern bloc days when tyres were currency for their riders when they came to the West, among the Barums etc there was a Soviet tubeless tubular. Can't remember the name, but it was a big, thick and not particuarly fast tyre. Puncture once and throw away...

I use tubulars and never realised that they were inconvenient until I actually started reading forums. The initial mounting is certainly a bit of a project but once fitted they have always been very uneventful as far as I have experienced.

Punctures are simply fixed. Remove the valve core, add some sealant, refit the core and pump up. Far easier than wrestling a recalcitrant clincher from a rim on a cold morning.

I'm not sure how removing the tube from a tubular would be an advantage as the tyre needs some airproof layer somewhere in it's construction.

Kind of, Tufo do a tubular clincher which is a tubular with a kind of foot on the bottom that allows you to mount on on a clincher rim (with the usual hooked bead). See http://www.tufo.com/en/tubular-clincher/. Tufo maintain they ride like tubs. However, they suffer in comparison to a tubeless tyre inasmuch as you can't just whack a tube in there when you get a flat; so like a tub you woudl have to carry a spare tyre. And they aren't cheap, I gather. And your rims still have a hooked bead so heavier than a tubular wheel and don't get same roundness off rim as with a proper tub (more light bulb profile).

Difficult to repair if they ever did go wrong. At least with a tubular you can unpick the stitching. (Though i don't think it's a particularly easy job).

I run tubs and I find I do puncture less than with clinchers. I have run some with sealant too, after fixing a puncture on the roadside with it. It then kept running fine till the tread wore out .

I thought Schwalbe had done this a while ago, but nothing ever came of it. 

I personally see this as an interesting option, and one I'd be all over like a rash.