For the COIN conflicts of the last decade they were very concerned with medical fitness when recalling reserves (even SELRES/TR), that was because they did not want to bring in someone who could claim an pre-existing condition to angle for a medical retirement upon exiting AD. It doesn't matter if it was pre-existing, you can still claim benefits once on AD (especially if the condition was aggravated or got worse).

IMO if the pop really hits the fan the DoD will be far less concerned with medical fitness for older, experienced personnel (especially staff qualified senior O's). I suspect there will be different medical policies for junior rifle carriers than those with other specific skills.

I've seen those kinds of waivers for high-demand low-density skillsets, even during GWOT. The hypothetical long-term potential cost of dealing with medical issues would pale in comparison to the requirements to conduct (or constrain) a ground war in Europe.

Politically it would be much easier to incur costs (that's what DoD does best!) then to deal with the political repercussions of a draft. Especially since the draft gets you mostly junior rifle carriers, not experienced leadership.