150Aerobat,
Your question is a good one and the answer is something that those who have latched on to the pro-NAS at any cost bandwagon dont want you to hear (you see, NAS is nothing to do with making it easier for pilots or even anything to do with Aviation - it is 100% politics and bullshiit from dick smith and his pied-piper ignoramii).
Thing is.... IFR aircraft can and do get told remain OCTA. If they are transitting from G Airpsace they do not have an automatic clearance. In fact (they wont tell you this at AOPA school) they have no more priority at most controlled airports than VFR traffic - in fact, a VFR pop-up at most controlled airports has equal priority to a 747 from LAX or Hong Kong. Don't believe me? Check your AIP! Do you know why most people don;t know this? (apart from propoganda and disinformation campaigns being run by the loony fringe).......
It's because, it is very rarely needed to delay an aircraft for clearance - for VFR or for IFR!
The phrase 'remain OCTA' does not equate to 'Clearnace not Available'. It just means that the controller is finding your flight plan details (or entering them into a data hungry network system if you havent flight planned : hint-hint--> put a bloody flight plan in people!), or has not yet identified you (radar). Once you are sorted, you wil only ever be delayed if a separation standard can not be applied immediately to other traffic in CTA, or you have a lower priority according to AIP. (i.e. Sydney Airport / Medical traffic etc.)
There is no black magic or how a controller feels about it.
Dick Smith doesnt say this in his rants - frankly I wonder if he even knows it.