Regarding your first paragraph, I must ask, have you done significant coding in Julia? Because an outdated sysimage is not really that big of a problem in practice. I have a sysimage which includes common big packages for plotting, numerical computing and some prettifying stuff I like like OhMyREPL. Then during dev time I add and remove packages, the compile time for those is significant enough to be noticed but not significant enough to be a problem. Because of the great composability of Julia, I'm guessing internally its using those big libraries and thus find most stuff precompiled for them. But I can't be sure about that.

Anyways, this is just my experience and my job involves a lot of waiting and stuff anyways so a couple seconds here and there doesn't bother me.