Only problem is that no one else supports it.
One thing that will help (once it's supported, heh) is the @supports rule http://dev.w3.org/csswg/css3-conditional/#at-supports . (Actually, it'll help even before it's supported, since you can put the "down-level" version outside the rule and then reverse the properties and do the new stuff inside the rule. The inner bits will be completely ignored in old browsers.)
Seriously the boorish comments about "no support yet" are like listening to fat client advocates in the 90s.
Cross browser support is not always necessary.