In this track plan, room for a turntable is created by increasing the width of both shelves by 3″. This is the track plan for the left side of the layout.
And this is the track plan for the right side.
This plan adds 1 right hand switch for a total of 6 right and 4 left, plus a Peco 12″ turntable. The plan also adds an industry siding.
I’m not troubled by the additional 3″ of shelf protrusion into the hallway as these shelves will take no more space in the hallway than track plan option 1 when rotated into vertical position. Increase in weight will be negligable as the expansion is mostly Homasote with an additional 3″ on lateral pine support members.
My strong tendency toward this design was implemented by ordering a Peco ON30 turntable today for around $100 shipped. Research is complete on how to bash this into a more realistic looking gallows style turntable.