Absolute to relative aiding

Hi there.
AFAIU, Ardupilot doesn’t switch from absolute to relative aiding. It can switch to relative from none aiding only.
Means, in case of GPS + OpticalFlow/BodyOdometry setup, once the drone loses GPS signal and continues relying on odometry only, it stills uses absolute aiding.
What is the intention behind this and what are the implications of switching from absolute to relative aiding?
Thanks.

Some features, like the one you described are still lacking because they are hard to achieve due to the sensors lack of precision.
That lack is not there because of a decision. That lack is there because no one has yet been able to provide robust working code.

GitHub merge requests with accompanying tests and proofs are welcome.

Ok. So, there is no intention.
Then, I was thinking about switching to relative aiding somewhere here.
Smth like

if (velTimeout)
    PV_AidingMode = AID_RELATIVE;

But I suspect it’d have been already done if it was that easy.
Any thoughts?