The last miner to mine a block can generate mempool blocks until a new miner comes along == the current miner.
So what about a race condition, stale blocks? What happens if two miners find two blocks of the same height and broadcast them almost at the same time? One of those blocks will become stale, but before that happens, who is making those mempool blocks?
As for the malicuos miner, there could be block size limits placed on the mempool blockchain just as is done on the core blockchain. But we would probably build the flexibility in from the start so that we do not repeat the current issue with the block limit. Yes, malicous intent needs to be addressed, but I think we can work the details out for that issue prior to implementation. In general it i not in a miners best interests to mess up bitcoin...
It isn't but there are always people who want to see the world burn... Or just mess up Bitcoin because they can gain from Bitcoin crashing.
Thanks for the comments :-)
No problem.