in summary
1. MM won't have disjoint tier (ie 5 to 2 tier X's and 5 9's to 1)
2. arty stun mechanic is being introduced as the final attempt in balancing arty (if we go by the dev stream commentary)
3. light tanks will have their tiers re arranged to have it -2/+2 like any other tank type and thus will make tourneys more balanced overall (no more bulldogs in tier 7 tourney's for instance)
in more detail and my opinion:
just recently, the changes to artillery, MM AND tier X LT's are coming together in one big update
MM won't give disjo