http://us.battle.net/sc2/en/forum/topic/9628133352#1Quote
We're looking to start testing more changes on a test map so we can better prepare to make tweaks if they’re needed in the future. Please understand: as always, we’re not proposing final changes with this balance test map. If and when we do decide to make any balance changes, we will definitely let you know.
1. Overseer speed buff (after upgrade)
TvZ feels quite balanced until the very late game when there are so many skirmishes and so many Widow Mines. We want to keep the really exciting gameplay while finding ways to help out Zerg in those specific battles. Having to micromanage your army in every engagement, morph new Banelings, manage 4-5 (or more) bases, and morph new Overseers can be a bit too much. So we’re going to test giving Overseers a speed buff after the speed upgrade is purchased, so that we keep the early- and mid-game the same while specifically helping out the Zerg in the later stages. They still wouldn't move as fast as say, Mutalisks, but perhaps late game TvZ goes more evenly if Overseers don't lag behind and get killed in most late engagements.
2. Combine mech ground and air upgrades
We don't think Terran is struggling, but do think mech in general has been weak throughout HotS. We tested this specific change a bit in the beta, and we have some idea of how much better mech will be, but a lot has changed since then, so we'd like to actually have players playtest it again.
Right now, it's looking like the only area where Terran might be weak is late game PvT, but it’s debateable. If so, this change would address that area, because upgrading Vikings that are really core in the matchup will also help with the Hellbat transition in the late game.
3. Vipers start with full energy
We’ve been discussing various options for the Zerg both internally and with top players and casters around the world, and we feel that this change might be a good place to start testing.
We don't know yet whether we want to increase the rate of Vipers’ spells, and thought it might be cool if Vipers come out of the box at full strength, so their first use has a much bigger impact. It’s possible that we can both increase the strength of Zerg in the late game and bring back a fun strategy that we’re seeing a bit less lately.
Again, please remember none of these changes are final. We're still constantly watching our ladder data and the highest level tournament games. As we all know, something that looks overpowered right now can change for top players in a matter of 1-2 weeks. We want to know as much as possible about how changes like these play out, so we’re ready when changes are needed.
Viper energy seems nice, I dunno about the mech upgrades..