If you look at the prompt while using a mirrored polygon drawing tool, you'll notice that it offers you to hold down the control key to create smooth nodes. This allow you to create a plan that has both curves and straights in the same poly.

Sounds like an interesting idea. While I have no idea if something like this will be made for CC4 or not, you can already today get access to all the data needed, so that should be able to be done with an add-on, meaning even if it isn't put into CC4 by default, it should be possible to write for anyone with a bit of programming experience and put in without PF having to add anything to pave the way.

Maybe not exactly the way you describe, but you can add large amount of text to your map using map notes. These don't display in-map, but in a separate window, but you can make hotspots to click to show the note you want, and each map note can have up to 8000 characters. Not quite unlimited, but room for quite a bit of text.

I do this frequently for atlas maps, for example, try downloading and opening the Southern Scar map from the atlas, and hit the Description link in the sidebar, and you'll see a description of the map appear. This is a standard hotspot that can be placed anywhere in a map.

Some more information in this blog article:

Kind of. The List command in CC3+ gives a lot of detailed information about entities, and it can be exported to a text file that shouldn't bee too hard to parse programmatically.

If that does not cover the need, it is also possible to write your own extension for CC3+ that can walk the entity list and generate whatever output you need, but of course, that does require a bit of programming.

If you name them sensibly, you can achieve the same (But you do need to use a command, not the GUI). Say you have a bunch of layers with different kinds of GM secrets, then you can simply name them GM Secret Doors, GM Secret Traps, GM Secret Secrets, etc. Now, you can toggle the visibility of all of them with TOGLF GM*, with the companion commands SHOWF and HIDEF. ('F' here means 'Filter').