They're limited by the 2-hour rule, no big deal. But we're approaching a difficulty adjustment, and if they happen to be doing this on the last block in this difficulty period, they will trigger a block storm.
Better fire up my storm-blocking miner again...
quoting nevent1q…zvsqA preventive block was successfully mined at height 2421214. The two blocks that followed had an interval of 31 minutes between them.
If those blocks had been mined at the same rate without the preventive block, there would have been another block storm! #bitcoin #testnet #[0]