I think that's the problem. We want them for Joes, but I'm not sure worldwide TF fans that don't give two shakes about Joe would actually care. The market for such a thing is constricted to simply fans of both Joe AND TF, and I'm not sure that intersection of the venn diagram is enough to justify the effort.
If hypothetically I'm not a Joe fan, I might only want them in a smaller scale, like hot wheels or something. And then there is also the problem of not being able to offer both factions the same treatment. 1:18 guns & walkmans aren't exciting, and 1:18 jets are expensive, huge, and kind-of already done... sort-of (SDCC). So you'd only have autobots, and it's tough to get collector momentum when you can only produce one side of a conflict.
Hardcore TF people would be very divided on these... like reverse action masters. TFW would have to split into two different websites, the "It's not a transformer is it doesn't transform" crowd, and the "eh, it's fun, so what" crowd. The more I think about it, the more I get dizzy pondering the reactions. I dare you to float this "over there" and see what kind of venom it elicits.