From a customer perspective, I think it makes sense to release models that no-one else makes. Not sure how realistic that is from a company perspective, but thought I'd mention it anyway. As there is minimal competition in the 1/56 scale market (let's not count the awful resin/metal combos that some manufacturers produce), I'd say there is a lot of scope for doing this.
As far as Italeri goes, they currently only produce the 88 Flak, Hetzer, Char B, Tiger II, IS-2, Puma, KV-1/2, M4 Sherman, Panther, Cromwell, Hellcat, M3 Stuart, Churchill, M10, M8/M20 Utility, Pz-III (late), StuG-III (late) and the Tiger I. Warlord also do the Pz-38(t) - not sure what else.