I know that there are plans to cache even more, but other than that I can basically only recommend to put distinct projects into proper projects (with a module and Project.toml). That will already cache precompiled code for that module, even between sessions. Having things in a script won't have that benefit. For experimenting with struct layouts, I've found that NamedTuples (https://docs.julialang.org/en/v1/base/base/#Core.NamedTuple) are amazing for prototyping, since they can be accessed via A.b just like structs but don't have the limitation of being const global.

The dynamism and flexibility combined with the compilation model is basically what leads down this path of recompilation, unfortunately. Since importing packages may change behaviour/invalidate some compiled method (that's what the SnoopCompile stuff in the article was about), it's nontrivial to just begin caching things left and right. You'd end up with an exponential explosion in the number of methods to cache, wasting huge amounts of disk space. That's not to say that there aren't more things that could be done, just that it's hard to do so.