HBASE-8701 and a lot of recent issues include good discussions about mvcc + seqId semantics. It seems that having mvcc and the seqId complicates the comparator semantics a lot in regards to flush + WAL replay + compactions + delete markers and out of order puts.
Thinking more about it I don't think we need a MVCC write number which is different than the seqId. We can keep the MVCC semantics, read point and smallest read points intact, but combine mvcc write number and seqId. This will allow cleaner semantics + implementation + smaller data files.
We can do some brainstorming for 0.98. We still have to verify that this would be semantically correct, it should be so by my current understanding.