I don't have time to read this thread, so I don't know if this has been pointed out already. In our upthread discussion about Cryptonite and the MBC (mini blockchain), I failed to point out that the unscalable (without centralized mining) Bitcoin blockchain (and worse for Monero) can never be pruned because it relies on GUIDs to prevent double-spend replay transactions (or am I unaware that Bitcoin's tx GUID somehow incorporates the block hash?). If anyone is aware of a solution for that please let me know. Because I think it is major vulnerability of the MBC. Has Cryptonite addressed it in some way?

In order to make sure the same signed transaction isn't processed by the network more than once, the block header must also contain a “lockheight” field. The transaction becomes invalid once the lockheight is outside the range of blocks which nodes are required to keep (lets call this the blocks “in view”), and same txid cannot be included twice in any of the blocks which are in view. This makes it impossible to use the same txid twice. However this solution requires that the txid is not malleable.