I tried tubeless on my Campy Eurus convertible wheels, swapping tires with a guy in a town nearby.
He tried my Tufo tubular clinchers, I tried his Hutchison tubeless w/Stan's sealant and valves.

I'm back on the tubular clinchers and he's back on his tubeless. He's happy, I'm happy.
The wheels came clean, no problem. He's a steady distance guy, I ride shorter and harder.

Pro's:
The tubeless ride better than my tubular clinchers, but about the same or a bit "heavier" than my regular tubulars.
They look nice, and have a little more cornering "tread" than the tubular clinchers, seem sturdier than my Pro Race's.
I agree with well biked, they "round out" a lot better, at lower pressure, than my tubulars, clincher or regular.
Weight-wise, about the same. Look like clinchers.

Con's:
All psychological, because I didn't have a flat. I did worry about having one.
I had less confidence about high-speed cornering, and jst didn't like the sealant idea.
I don't "pre-treat" my tubulars with sealant, and don't like it as an idea for fixing a flat.
(I once treated a car flat with Slime, and the vibrations over 35mph were crazy bad).

Some of the guys at REI and Performance like the tubeless idea, a lot.
I think I'll wait a while, and I think yes, it's the future for a large % of riders.

To me, right now, they're the same as clincher tubulars, ride a bit nicer, but are messier.
Both take longer to mount and remove. Both are light, and both cost more.
However, the clincher tubulars could care less what rim you mount them on, and are clean.

For 650B applications, I think I may like it more.
There is so much more tire, and so much less pressure, maybe I'd have less anxiety.
I'm also sure if I had to change, and got used to the installation and flat tire procedure, I'd be fine.

My supply of wheels is a hand-me down market, and until they start showing up in that market, it's not an issue for me.

Down the road, sure. Of course, it would be so much easier to have the whole fleet on one or the other.
My favorite tires that are tubed are almost all a major PITA to get on the rim, and pinching tubes happens.
I prefer tubulars, but that requires having tubular wheelsets, expensive tape, and higher-dollar tires to get good performance. I like tubular clinchers, but have not found a reasonable one for racing.

If the wheel build is nice, and I can get past the idea of sealant running around in there, I don't see why not.