To be honest as a regular user of this route from our local station at Bempton, I would rather it was left alone. Its reasonably reliable, and uses 170s for the most part which are fairly comfortable. From a passenger point of view I cannot see what benefits moving it (back) to TPE would bring.
Back in the early 2000's the Hull Scarborough route was partly operated by the precursor of TPE as an extension of the Manchester Hull service, including the calls at the small stations. Whilst this gave better connections to West Yorkshire connections south were more difficult.
I also wonder if 185s would be subject to lower speed limits as they are quite heavy.
The current hourly service from Scarborough meets most peoples needs. The single line section from Bridlington to Hunmanby rules out anything more than an hourly service each way. If you are travelling south then the connection at Doncaster for the ECML is fairly easy, and for Birmingham and the SW a change in Sheffield. The more difficult journeys are North, but unless you had a new track giving access to Brid-Scarbourough from York which isn't going to happen joining up the routes isn't going to save much (Edit, and missing Scarborough isn't really an option anyway) and will potentially import delays from further afield, which will in turn then affect the single line sections giving knock on delays and making the service less reliable for local travellers, who are probably over 50% of passengers.