How likely for a National Guard Officer to switch to Active Duty?

2LT (Join to see) Take a glimpse to the following link. I have not fully read it but it could possible have the answer you're looking for. https://www.hrc.army.mil/OPMD/Call%20to%20Active%20Duty%20Program

I would say it would be difficult since you aren't qualified yet. I may be wrong though.
I am confused about you not being able to get a school date though. Are you OCS or ROTC? MOSQ(or Officer qual) usually takes highest priority for NG(USR looks bad). If youre ROTC funding should come straight from NGB. OCS is State funded.

I'll caveat COL Charles Williams and note there's always intake of JOs even during downsizing albeit at a reduced rate. The services always need young/junior intake to preclude holes in structure that can last 20 years. So they just turn the spigot down a bit. The math works out like say you have 100 and have to get to 80. They'll push out 35 while bringing in 15 to ensure no serious gaps are created later. Typically they'll undershoot both numbers because some wonk in the Pentagon says there's not much severance, blah, blah, another unfunded mandate. That said, whatever they take in, they can be real choosy so you're in a competition with some advantages and some disadvantages that more knowledge folk on the Army side can weigh in on.