I've been reading this as interested to see others thoughts on it. And in many respects I am regurgitating what Vectorline/AIRAC have eluded to.
The one thing about this is everyone seems to accept a/c are identified under a basic service, they do not need to be identified and if you are working a number of a/c who are positively identified under a traffic/deconfliction services, maybe someone on a SRA, couple of others being vectored for final approach and say maybe 10-15 a/c a mixture of local based out general handling & transit a/c on a basic service are you really going to try and identify all of those a/c increasing you workload massively? This is not an uncommon scenario where I work.
So what gets drops instantly when busy, calling traffic to basic service a/c, so why lull pilots into a false sense of security and give them above what is asked on a basic service when you are quiet and able to do so because the day you can't is they day they will not be keeping as good look out as they should.
Have you also considered some pilots (especially when out with students) and in asking for basic service do not want to hear ATC giving them information they have not asked to receive and are trying to teach there student the art of looking out?
Furthermore, what if you give traffic to an a/c and an incident does happen, its on a basic service and you have not positively identified (yes I know you can still identify on basic and not say) maybe in an area of high activity, and it turns out your actions contributed to it?
No ATCO will ever intentionally do something that may lead to a incident, and at the same time not step in if you feel you need, but why muddy the waters and keep FRISSING to basic service a/c (as may do at present under a FIS) when the whole point of them being rewritten is to try & stop the ambiguity?
But then this is air traffic and nothing is ever right apart from what's in ones own mind.