As mentioned elsewhere, Revit and ArchiCAD go through a process of reading from component libraries when a the main file is opened. Being more 'BIM oriented' from the ground up, most content in their models are component / objects so finding and loading quickly is optimised by embedding as much of the library content as possible in the main file.

Mstn is more old skool being CAD-based and is optimised for lots of one-off geometry (Bravo!) and federated (Bravo!) but also accommodates smart parametric components (Bravo!).

I think Mstn's caching mechanism only starts to cache a Ref attachment after it is loaded. The Cell Library tool could maintain a list of recently opened Cell libs and automatically load those Cell libs in the background as Refs that are hidden in Ref Dialog.

Alternatively, you could just define a new ConfigVar MS_PROJECT_CELLS, and auto load the listed Cell libs when a dgn is loaded. This would replicate the Revit / AC project loading process.

See previous discussion