The closest app I've seen to this is the Trimble Connect App.
On an iPad, want to be able to:
1. view the design in 2D superimposed over the pdf plans.
2. view the ttm surface in 3D combined with the dxf lines draped over the surface
3. Create a cross section slice of the surface with nodes labeled for named linestrings
Our controllers are sync'd to TCC, so it would make sense that the viewer references projects in our trimblesynchronizerdata filespace. Annotations would have to be kept in a separate file per user.
Our foreman and engineers have no access to the models except when looking over the shoulder of the grade checker or standing in the cab of the dozer to view the display.