First, I have some sympathy for this idea.
However, I’m not certain I support moving this into the core, unless it’s the only way to make it happen. I don’t use Projects normally. In my use, EmEditor is a super powerful, hyper-fast, syntax highlighting text editor, not an IDE. The editor’s speed is the thing that keeps me coming back. When files open at the speed of thought, it’s hard to use one that makes you wait, even if for only a couple of seconds. The more built-in functionality, the slower the editor will be, and the less attractive for my usage. If the idea would work as a plug-in (and I confess that I don’t know what the limitations of a plug-in are in this area), I would prefer that.
That said, I admit to not using these features much, but I might use them if they worked better together. Having the workspace global across all open instances of EmEditor makes it not terribly useful for me, so I have to use scripts to support a similar, not as useful, functionality. Having used Atom and Visual Studio Code before dumping them in favor of EmEditor does make the concept of a Project Folder attractive, although not as the central file management feature, and I hesitate to ask for the complexity needed to make something like that optional.
Not exactly what you’re looking for, I know. But I’m not sure that merging all of those together into the core will be useful for those of us who don’t mainly use EmEditor in the “project” aspect.