Finally!
iOS 8.2 Beta 4 has fixed the Bluetooth connection issues, at least it has on my IPhone 6 Plus and hopefully I would think for everyone else.
Drove fro home to work, approx half an hour and no issues.
Please note this is on 8.2 Beta 4 Developer which will be a while before it is released to the public.
Next public release I think is in a week or so so rumor has it and will be 8.1.3
Whether Apple have fixed the problem for that release will remain to be seen, but my guess it will be