Currently each assembly created with an assembly definition file is given a reference to *every* precompiled assembly (plugin), as shown in Figure 3 of this page:
This results in a rebuild of every assembly when any precompiled assembly is changed. This is a problem in a build environment such as ours where the bulk of our code is built from Visual Studio and copied into the Assets folder in a post-build step.
I would like to suggest that assembly definition files can specify explicit dependencies on precompiled assemblies, rather than implicitly depending on all such assemblies. The assembly definition editor perhaps also needs a checkbox to opt out of all the implicit dependencies.
Note that this is not just a mechanism to improve script build / import times, but also enables us to manage dependencies correctly between systems, to prevent unwanted dependencies between modules.
This won't prevent loose script recompilation, but we can ensure all scripts are in assembly definition files and that there are no more loose scripts.
I suggested this idea in person to Richard Fine at Unite LA 2018 and he agreed that it seemed like a good idea.
If you have any questions about how we would like to use this feature, don't hesitate to get in touch. Thanks!