Yep.

Can u elaborate? The research I am doing shows the underfloor heating going under shower, so that tells me it is possible, not that we are doing under the shower but just have concerns about heat and the membrane and how to do it, thanks

If you have a subcontractor installing the heating elements, you should have them confirm this. If you are doing it yourself, you should contact the manufacturers of both products and have them do the same.

I don't know of any issues with shower membranes over radiant floor heat. The issues are really in the radiant floor element if it is electric where you cannot use line voltage elements in the shower, they need to be 24V.

My question is why extend the waterproofing beyond the shower curb if it isn't going to a drain? The waterproofing may protect the subfloor under it, but only by migrating the penetrated water to a location where there no longer is any more waterproofing and you'll just have a concentrated moisture problem at that line.

No curb to this show, walk in, curbless, so safe to carry it out of the shower perimeter a foot or so.

FYI, contacted both suppliers and even got a written guarantee that it's not an issue

If your using a surface membrane than there is nothing to worry about if you waterproof the entire room. We have been installing heat in the entire bathroom since we switched. We will run a wired system bedded in self leveling cement. This gives us the flexibility to concentrate or eliminate heat in strategic locations around the bathroom. We will avoid under a floor mounted toilet, run thin under a vanity, concentrate 2 feet outside the the vanity and 2 feet outside the shower.