So I've been building a metric crapton of Shermans lately as a part of several armies (US and Soviet) and see several gaps in the existing Battlefront range - most of which I think would be easy for them to close at this point. I like the fact that we have the M4A3, M4A3 (late), and M4A3E8 variants as discrete offerings. Unfortunately we don't have quite the same options for the M4A2 or the other Sherman variants. Fortunately, Battlefront already produces most of the required components, so it should be easy for them to fill the gaps if they have the will to do it.
You could, for example, create a late 75mm M4A2 by combining the M4A2 76mm hull with an M4A3 (late) 75mm turret. You could also create the late 76mm M4A2 by combining the current M4A2 76mm miniature with the M4A3E8 76mm gun with muzzle brake. Given that there are already multiple track systems available in the online store it seems like it should be easy for Battlefront to offer the hulls, turrets, and guns separately or simply create "package deal" for specific models only available through Special Order.
I don't hold out a lot of hope that I'm ever going to see any direct vision slot hulls, so I'm resorting to conversion and casting to go that route for my Kasserine Pass army. However, I'm working on an emcha army and want to model some of the very late M4A2 76mm with the muzzle brake, and would love to just be able to pick up the guns separately from Battlefront.