Certainly worth a try but getting to 200 good sectors will be a challenge as this is a high number even for the ZX to achieve.
Replacing R4 and R5 on the ZX Microdrive header board with 330R resistors (instead of 150R and 180R respectively) as per the QL header board equivalent design seems to help (improves the ZX Microdrive performance on the few ZX drives I have working as well). The purpose of R4 and R5 are undocumented but may affect the record equalisation (anyone have any further info?).
After a bit of playing around this afternoon I did manage to format a cartridge on an external Microdrive attached to the QL. However, I had to bypass the internal drives and jumper COMMDATA. Trying to get a successful format with the internal drives present was not possible with the drive setup I had. Formatting was very hit and miss with a very failure rate. The same cartridge formatted consistently OK in a Spectrum setup during the tests.
The ZX drive was modded as mentioned previously. Reverting to the original ZX design lead to 100% format failure so the new values for R4/R5 are needed.
So it is possible - sort of. I can only conclude that the internal drives passively load the Microdrive bus in a way that leads to instability. Maybe one of the reasons why external QL Microdrives didn't eventuate...