I think you're spot-on, Q630/LC6xx and PowerBook 190 were transitional, low end market tier offerings and almost without doubt, solid plans for upgrading the logic boards in their brand new case designs. They utilized the best of the old married to the newer technologies to come. The shift to IDE may have been a short term cost saving strategy for those models, but was without doubt a sign of things that were far too long in coming to the Mac.Does it make the 6200 a road Apple? I don’t think so. It makes the 630 a last-edition, state of the art 68040 machine. The 6200 is just a regular PPC with the limitations of the 603cpu.
PowerBook 150 fills the same low end market tier gap in the 68030 to 68040 transition I think. Marrying that series case to IDE and vastly expanded memory over previous generations via Duo Memory Card support was brilliant. Limiting it to passive matrix grayscale display held it back from stealing sales from the Blackbirds at the high end. PowerBook 150 is arguably the most powerful of the 100 series due to its far and away higher memory ceiling.