If full nodes do not require seeing the data to consider a block valid, then the data simply doesn’t exist as far as Bitcoin is concerned. It is exactly equivalent to a marker “increase this transaction’s data by X weight”, for no purpose except wasting fees. The system cannot even prevent someone from committing to SegData that literally does not exist, so there is not even a possibility of reliability, even if all nodes were perfectly altruistic about it (a very dubious assumption). With that, I don’t see why anyone would be interested in using it, and even less why the Bitcoin ecosystem would bother with its complexity.
Never thought I’d end up agreeing with @cguida on matters of blockchain data storage, but here we are.