Thanks for the reply Michael.

"The big problem with traditional layers where the layer itself has its own on/off property is that it greatly restricts flexibility. You can no longer show just an individual object you have to show the layer and all other objects on it then get shown too."

This has already been solved in most applications using nested layers.
In Blender for example the equivalent of layers are collections. You can have a collection with multiple objects, that you can individually show/hide, or show/hide the entire collection. Moreover, you can show/hide a single object's sub-geometry. And of course you can move objects between collections, or have multiple collections nested under another collection.
As you see, it adds tremendous flexibility for organization/selection/viewing, not to mention that it's the industry standard way for complex applications, and one that most people are familiar with.

All of that could work in conjunction with MoI's "types" concept, but with respect to the "active" layer. I'm not saying it's straightforward or easy to implement, but I'm sure that if you give it some thought it could turn out to be a very powerful feature.

Anyways, it's just a suggestion. Keep up the good work!