Aside of the nonsense about 'MiG-23s', this is actually an issue that should be taken seriously, Adam.

The Daesh has captured at least 25 MiG-21s (of different variants) at Tabqa, plus 2 at Ksheesh ('Jirah').

Additionally, it has captured perhaps as many as 13 L-39s at Ksheesh.

Of course, most of planes in question are long since derelict and of no use: indeed, the two MiG-21FLs at Ksheesh were posted as gate-guards already about 10 years ago. But, several others were in 'near operational' condition when seen for the last time.

Except for planes, photos and videos released by various Jihadist idiots there have shown stocks of air-to-air missiles, UB-16-57 and similar pods for unguided rockets, and light bombs of Soviet design. There is little doubt that they've captured stocks of spares - plus an intact radar station nearby.

Summary of what they've got:
- planes
- spares
- weapons
- radars necessary to guide pilots of these aircraft.

Now, the usual Western prejudice would be that 'barbaric Jihadists' have no clue how to operate such complex pieces of machinery like 'MiGs'. Actually, not only that especially L-39s are easy to operate (just ask all the private pilots in the USA: they own more L-39s than all the air forces around the world), but MiG-21s are relatively easy to maintain and operate too (exception is landing at speeds higher than those of Space Shuttle).

More serious is fact that when one monitors various Jihadist internet appearances carefully enough, it's obvious they're looking for and recruiting people with technical and electro-technical skills, i.e. technical personnel with military background. Several cases are known of them forcing captured Syrian military personnel to work with them, or even hijacking Syrians, Turks, Kurds and others with required skills to work for them.

Furthermore, Daesh is claiming to be operating several helicopters supposedly captured in Iraq already since June. While this is not true, it points at the fact that they are eager to obtain a sort of 'air force' capability.

Combined with the fact that the Daesh includes a large number (over 1,000) of ex-Iraqi Army and Iraqi Air Force officers, with enough related experience, that it has captured enough military bases in Iraq and Syria to find the necessary documentation, means that the Daesh is 100% sure in possession of necessary technical documentation too.

Overall: they have the wish, and now they have equipment, and are likely to have the skill necessary to overhaul and maintain, and then to fly these MiGs. And they've been left two months to do something about them (time-frame between the capture of Tabqa and the start of US attacks on NE Syria).

And finally: the Daesh is lot less keen to run suicide ops than AQ, for example. That's one of factors making it much more attractive for all 'potential recruits' in comparison. So, I doubt we're going to see the emergence of some sort of a 'Kamikaze Air Force'.

On the contrary, while they are unlikely to grow an 'USAF-equivalent/counterpart' in a matter weeks, months or even years, gauging by the fact that the Taliban have managed to establish and run a small, yet operational and combat-effective air force under precisely the same circumstances back in the 1990s - and that while having a lot less money, and far lesser global reach than the Daesh - I would say that one should take Daesh's efforts in this regards damn seriously.