All true, though the original release of the Constructicons was no less common than Ultramagnus, so I think they would realise there is a decent market.

The Glacier bot combiner that we've seen in pics will be a risky propsition in itself, as it's not directly related to Transformers like the other upgrades are. I would think they would want to test the waters more before they release something that ambitious.

There is always the possibility the next release might end up being a Devestator upgrade that is less ambitous than Crossfire.