Yet another LNP gimmick. Does the Borg think voters are stupid?
Building a line from the Sunshine Coast to, just the Sunshine Coast would be a bad idea, and not cost effective. For starters it wouldn't link the Sunshine Coast with Brisbane, which would be a major source of passenger loading. A depot would have to built on the line as there would be no access to other depots. Trains, and track maintenance vehicles would have to be delivered, and transferred (for overhauls) by road.
If the Sunshine Coast line was to be built in stages, then starting the construction at the Beerwah end would make a lot more sense.