If this becomes popular, then over time the number of bitcoins frozen in NFTs would become too large for the blockchain to continue to function fully.
this may consider a new kind of FORK that could happen anytime in any blockchain system. if a feature become popular, this means there was a valuable function in it, isn't it?
and why you call it "frozen" bitcoins / alt-coins? they just do not merge into other coins, so lower / higher amount of fees related to the block size may be needed to get processed. market will find its way.