I thought I'd share my experience in case it becomes useful...
I decided to move from BT Phone and Broadband to Sky Talk and Fibre + TV so I went ahead and placed the order successfully... but later on the online tracking said there may be a problem with Sky Talk/Fibre.
I called Sky and they say the Fibre order has incurred an exception. In this case this was because BT rejected the order claiming the DSAM has no free ports.
Given my exchange has only just been enabled e.g. my phone number allows purchase of a FTTC product before it said June, I'm thinking:
a) its just a matter of out of date systems (in this 2012+ world)?
b) my exchange is accepting orders but not yet active?
Exceptions are said to be handled daily between Sky and BT (openreach) so I hope its the former (a).
I'll update as I'm informed.
Any suggestions on questions to ask in case its not a simple .small delay ... resolved... happy scenario.