Actually Crossmark is a really good rear tire for tubeless, just the regular version. Any tire can get a sidewall cut under the right conditions. I got a sidewall cut on a new Specy Fast Trak Control a couple years ago, it was brand new. Since then I have rolled 100's of miles on Fast Trak's without issue... So you can get an armadillo/snakeskin/etc some other kind of heavy-built sidewall if you need it for really rocky conditions, just a reality check on was that a fluke, or are Crossmarks now forever an unsuitable tire?
For the price of an Ikon, you can buy two Crossmarks and throw one away if you get a cut.
Mavic wouldn't be my first choice of rim though for a tubeless conversion.