LSB 4.0 allows gzip rpm payload compression only. At the same time bz2 and lzma are widespread nowadays. We have to decide which rpm payload compressions have to be supported by compliant distributions/can be used be compliant applications and reflect the decision in Moblin specification/documentation/package creator.
We'll need to figure out which ones are widely enough actually used that they aren't going to cause compatibility problems, and then allow them. We did try to add bz2 to LSB but it got turned down, but that's kind of irrelevant to this question. I think lzma may be the outlier, but only a survey will really answer this.