I'm a HUGE fan of the way Playing Now works currently, so I'd resist any changes to this system. The basic idea of Playing Now is that it is
THE LIST that is "Playing Now", shown in the order it will play.
This simple idea allows some pretty amazing flexibility. You might not use some of it, but I sure do! For example, if I have "Shuffle Mode" enabled, and I play some files, I can then quickly go to Playing Now and re-order them (or, what I often do, browse around my library and add specific tracks as "Next To Play", and then let the rest play shuffled).
None of your ideas really conflict with this idea except for maybe #4. But, to be clear, the one thing I think CANNOT change (or should not) is that Playing Now should ALWAYS be a list of files, listed in the order that they will actually play.
Okay... That said. Onto this:
5) Ability to add a playlist to a playlist.
You can organize them already. Simply add a Playlist Group, which acts like a folder for Playlists. What do you want that can't be accomplished by this?
2) The option to have certain things like shuffle be playlist specific.
If you want a particular playlist to always be shuffled, you'd be better off using a Smartlist instead (which you can have always shuffled). The easiest way to do this, and still be able to pick-and-choose particular tracks is to build a Smartlist based on Keywords.
So, you make a Smartlist with these rules:
[Media Type]=[Audio] [Keywords]=[shufflematic] ~sort=Random
That will show ALL Audio files with the "shufflematic" keyword (which is also what I named the Smartlist), in a randomized order. You could add a track limit too if you want it to only show 100 random tracks with the keyword. If you REALLY want to not use Keywords but you want pre-randomized versions of existing Playlists, you can also link a Smartlist (or a View) to a static Playlist. Simply add a "Playlist" is any rule and choose your static Playlist, then add a Shuffle modification.
The whole idea in MC of Playlists is that they are manually-built ORDERED lists. If you don't want them ordered, then you are almost certainly better off building a Smartlist or a custom view.