What is the reason to not eliminate the pending-block at all?
I mean, the PoW for receive is already lower, making possible to receive that fast enough. Also, it's using the height of the block, not the previous-hash.
What is the reason to not enforce that every "send" most have a "receive"? I mean, the only valid "send" is that one that has one "receive", otherwise it's considered invalid.
The only downside is the need of both wallets be online. However, it'll make the pruning much easier and will make the old whitepaper correctly. Because without pending-block we can get only the frontiers. The "new pending-block" will be something like the mempool, which is not persistent.