Doesn't SDO require the guard and driver to be able to get out onto the
platform, so having the front car off the platform may not be an acceptable
solution even if the signal could be moved.

I was under the impression that they were planning to get rid of guards
on the NLL. Although that wouldn't help the driver, might certaintly help.

I'm guessing rules on LU are different, as there's a station on the
Northern Line IIRC where the front set of doors are not opened.