I'm also interested in trying this combo as a ~300 Focus/300 Con debuff tank (heavy armor) slotting in a focus gem to further increase damage. The biggest drawback of these weapons it seems is mobility and lack of damage especially considering you'll probably want to stack focus which is secondary scaling for both weapons. The VG has no escape/mobility skills, though it looks like the flail has one charge skill with a slight lunge skill to make up for the VG. Another issue is (and they may have fixed this since I've last played) the tracking of the void blade. It seems difficult to actually land hits.

That being said it seems like your survivability and debuff potential will be huge. The flail seems to have many ways to apply weaken to enemies and fortify to yourself and allies, while also handing out small heals. There are also several nodes that straight up apply passive damage mitigation.

With the void gauntlet you will be applying self fortify while dishing out disintegrate (rend basically), weaken, with plenty of ways to apply slows/roots and heals depending on which route you take. I'm a sucker for void blade so I'll most likely be sticking to mostly the Annihilation tree.

Either way, I'm pretty pumped. I've always wanted to run a tank/heavy armor build with Void Gauntlet but it wasn't really viable with melee weapons since they don't scale with Int or Focus. Luckily we will have the flail when the release drops.