Thank you for the reply. I think there are a few points I’d like to address before the proposal is overlooked.
Within the retention window (288 blocks) full nodes require the data. Absent data cannot be accepted. Existence is enforced network-wide at inclusion, exactly as for witness. The optional part is re-validation after burial, the same trust model as assumevalid, except a SegData node can drop the entries rather than have to keep and skip them. They gate no spend, so are never needed for validation again. Consensus not needing the data is the point, and what makes the download-skip safe.
Therefore you’re right that there’s no guarantee of perpetual retrievability, though under default archival that is a question of redundancy rather than availability. What is enforced in full is proof of publication at inclusion, which is exactly what witness gives you. SegData keeps that while removing only the obligation to retain.
Carriage is already happening under the witness discount and will continue. The weight you call purposeless is weight a small node on a metered link must download during IBD and keep on a constrained disk today. This proposal (which i believe is less complex than segwit and follows in its design lineage) offers an alternative which lets this or any other node skip historical entries during sync and retain only the window, while still fully validating the chain and serving the monetary history. Pruning doesn’t offer this. So a question arises, is whether requiring every node, including the smallest, to retain abritrary data forever is better than letting it drop it?
I appreciate your time.