I've thought about a soft fork that can help storage costs.
Why don't we force miners to embed the height of the TX Merkle tree in the first two bytes of the 4-byte block header version?
It would have two advantages:
It'd fix the leaf-node brute force weakness (CVE-2017-12842), which is currently fixed only by standard-ness rules but not by consensus rules.
Similarly to the description in BIP 141, we can introduce a type of node that is neither a pruned node nor a complete full node, but they'd have
txindex=1for transactions with unspent outputs. Those nodes would first store full blocks. When the next block comes, using their txindex they'd look up the block, find the transaction and check if all outputs are spent. If so, they would remove the transaction from the storage of that block but only keep its hash. This would save a large space since it seems to me that most scenarios of querying a txindex-enabled node would usegettransactionon transactions with unspent outputs?
Any comments? I don't think this is worth sending to bitcoin-ml.