The print/prepress industry has a long history of devices with asymmetric resolution, or higher resolution in monochrome versus color (similar to 4:2:0 pixel format used in digital video).
Considering professional print/prepress machines last 20 or more years in-service you have to handle just about everything.
For example, an image with pixel dimensions of 1800 by 1200 and a “DPI” metadata value of 300 will print with a physical dimension of 6.00 by 4.00 inches.
Many film scanners for instance are say 2400 dpi vertically and then some other DPI value horizontal depending on the film or picture format. Anamorphic lenses are used to scale a wide-aspect image onto a 4:3 sensor.
Some scanners and printers even have different DPI for different color components.
This is all entirely in the hands of Adobe.
My point still holds for CMYK though — bandwidth optimisation is rarely a concern for intermediary files. In fact, it's common to see compressed files rejected for being "low quality" based on file size and with no regard for the actual image fidelity. In this industry, formats like TIFF are sufficient.
If one was to propose a replacement for TIFF, it would need to support a lot more than just CMYK. Off the top of my head, it would need full alpha, embeddable profiles, 16 bit support, arbitrary channels, spot colours and vector clipping paths.
(As for CMYK conversion: even if you are touching up photographic colours for CMYK, this should be performed within the RGB space and soft proofing. The final conversion to CMYK should occur at print-time unless there's an excellent reason otherwise, e.g. if you are applying CMYK-inspired graphic art effects.)