I know nobody asked this question, but I was so happy to have figured something out, that I thought I'd share. Bear in mind this is not my oriignal idea, but here it is in simplified form:
1. To creat an eventual custom folder(s) in the Project Browser, first go to Manage tab --> Project Parameters --> add... and add a new Instance Parameter (Identity Data) -- whatever name you choose for the parameter, not the folder. Add it to both the sheets and views categories. Click OK etc to get out of it.
2. Under View tab --> User Interface --> Browser Organization --> Views tab --> New... type in same thing you named your parameter and click OK. Then group by Family and Type, then by your parameter (leave the rest alone), and click OK. Back in Browser Organization --> Sheets tab, type in your parameter's name again and click OK. Then group by your parameter (leave the rest alone) and click OK etc. go get out of it all.
3. Now in the project browser, right click on Views --> Type Properties, and change the type to match your parameter, and click OK etc. The only difference at this point are the extra folders with the ???.
4. Now highlight a view and look at its Instance Parameters under Identity data, and it should be blank. That's where you can type in a new folder name and Apply it. A new folder with that name will appear in the Browser, with that view moved into it! That's the simplified version, but if you have lots to classify this way, you may want to look into a View List (Views tab --> Schedules --> View List) so you can run down through it and add folders and classify views to your heart's content.
5. I also included the Sheets category back in steps 1 and 2 in case you want to do something similar with the sheet sets. However, I also discovered when you highlight a sheet, under its Identity data you have the ability to either assign it to a shortlist of disciplines, or create one of your own. So when you right-click on Sheets and choose Type Properties, you can either choose your parameter and go from there, or you could choose By Disciplne. You can have Views do one thing while Sheets does another thing!
I know I am not answering anyone's post, but it's one of those things that eluded me for awhile until I finally found the time to investigate. I am happy with the results so I thought I'd share, on the off chance someone else is looking to accomplish the same thing. If anyone out there has a better way, I'd love to hear it too. Never too old to learn new stuff!
If by some odd chance my nattering was useful -- that's great, glad to help. But if it actually solved your issue, then please mark my solution as accepted