Man I am absolutely baffled!!! - I removed mac s/n (clover injected one by default)removed Bios version and Bios date, rebooted, checked they weren't in the config.plist and was still abled to log into iMsg/F-Time. I can only conclude that the onus is more to do with establish Apple ID's and here on late newly created ones are being flagged on non Apple devices i.e Custom Macs.
I really don't want to go down the road of creating a new ID just to prove that theory just incase it compromises my account. Where to go from here I really don't know, I tried to source some info from a colleague who is employed at a Genius Bar and they were just as baffled, their take on the matter is since around the last update it seems Apple has placed preference on trusted ID accounts over new ones, so we are still in the dark here.
I can't envisage what the outcome will be apart from locking out Custom Macs forcing us to buy Macs because although I build my own, I have quite a lot of purchases from the App Store, plus a mini iPad and both my wife and I owned iPhones from iPhone 3 to the present model as I am sure a lot of members here do as well. Are they really willing to go down that route - It would be a case of cutting off your nose to spite your face so to speak.