I seem to recall hearing something about promotions for your crew being non-existent.
Is that still the case? or did that 'issue' get fixed?

I can't remember for sure, since it happened a long time ago, but I remember one of my guys getting a promotion. I believe it was after I shot down three fighters(with a keyboard, hah! ...my joystick broke :() in one mission controlling the guy. It's rare, but it happens.

After I flew some tour missions I saw promotions in crew files in office. It happens automatically I believe. At least in Bomber commander campaign. Never played as Squadron commander.

Must be very rare then, since I can't find anything about any issues, wish there was some sort of diagram around.

its in commander office in crew files with missions history.

No, I mean like something that tells me how many kills or missions or such a specific crewman needs for promotion

There isn't any. It just happens. There's no "EXP bars" or any such thing.