On the drop-in filters, wouldn't they keep making (at least, selling them) for a while even if future lenses wont use it? There's going to be a lot of lenses in the field that might need spares/replacements. Having said that, the alternative isn't any better - that the supply chain is badly planned.
Canon 1D, 300D IR, 450D full spectrum, 600D, 5D2, 7D, EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 70-300L, 100-400L
EF-S 15-85, TS-E 24, MP-E 65, Zeiss 50/2 macro, Sigma 150 macro, 120-300/2.8 OS, Samyang 8mm fisheye