I used ultegra 6700 wheels set up tubeless with a Panaracer Cinder X in front and a Maxxis Locust on the back last year. Worked great. Ran 45 front, 50psi rear, may go a few PSI lower this year. (I'm 73kg) So no, you can't run pressures you normally would in a playing-field cross race, but still significantly lower than with tubes. Even with tubulars I doubt anyone is running much less than 40psi since the risk of bottoming out on the rim on Whernside is pretty significant. I at least
felt more confident descending whernside thanks to lower pressures and grippier tyres than the Land Crusiers.
There is a risk of burping if you are not using tubeless ready wheels or tyres, but this can be avoided with proper set up. This is a good how to article:
http://www.cxmagazine.com/going-tubeles ... mendationsThe key concern is making sure the bead is tight, and having a low bead-to-rim bed distance.
I actually punctured my Cinder X on the front this weekend- something cut a 5mm hole in it, but the Stans fluid sealed it up- though it took a minute to standing with the hole at 6 o'clock since it was about the largest hole that fluid will normally seal and it takes time for the fibres in the fluid to build up. But still much faster than changing a tube. I had 40psi in them when I started, and lost about 10psi.
I think the more people try tubeless and see the benefits- more people will use them. The only drawback really is burping, which can be avoided with proper setup. You also will not be flying around corners at 3PCX like you would in a 'normal' cross race, which is where burps usually happen.