We have recently started the process of switching our development methods to sfdx and Unmanaged Package2 setup. We use interdependent packages ex: Core package is used as a dependancy in a feature package
Right now Illuminated Cloud includes Apex Classes from package dependancies as always but shows no code and only class declarations. Now with Unmanaged Package2 metadata and code can be changed on whatever environment it's installed but needs to be updated eventually in the package itself to keep changes since upgrades will wipe the changes out.
I came across this post in the Package2 community in Salesforce which describes the problem: https://success.salesforce.com/0D53A000047u42f
Where minor changes needs to be made to base code inside an unmanaged package but as is Illuminated Cloud 2 only includes the code (even though it's fully changeable) in the OfflineSymbolTable
My proposal is considering the possibility on actually allowing us to pull the classes and modify and push again even though they are within an Unmanaged Package.
I do realise this seems to be a problem from the DeveloperConsole as well so i am not sure if this is realistic request at all