Apple
If the DWP contact your GP and it is quite rare for them to do so in regard to PIP then it will be a GP Factual Report, there's a section towards the back of the PIP Claim guide that covers this.
I haven't seen any official update on the 2017 timeline, although I have seem comments about it being extended to 2018, our only reference point is the ESA transfer process which was due to finish in April 2014 and is still being carried out. My best guess is 2020.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems