for ex. http://www.keil.com/pack/doc/cmsis/svd/html/svd__example_pg.html The file describes the internal periphery register structure of arm and other µC (i know the files also for atmega/xmega)..
I think some of the embedded forks of cb has a parser for this added to the wizard.
i don't know the UI yet.... some kind of property grid, it should have the possibility to use drop down menus,check boxes and text fields. Custom controls like leds (red dots) would also be nice... A search field would also be needed, because there can be ton's of register and flag names
Unfortunately the propgrid is the best ui for this, but I'm not sure I like this control. Especially the migration from 2.8 to 3.x.

By bloating i mean code/ binary size... More things to maintain for the main dev team
Of corse it is possible to add it at the core and make it configurable, but i don't like the idea to add something to the main plugin what is not needed for the core.
Don't worry too much about this. The cpu registers window needs improvements. If you make them general enough it might be good for all users.
And there people which will be happy to use something like cb, instead of the vendors ides.
Because there is also potential for more logging/debugging like:

I don't think this functionality should be in the core. But if you want to use codeblocks (i think there is no really nice, cross platform and fast IDE for debugging embedded systems out there) for embedded development you "need" this things. It would simply be nice to have somehow an interface to gdb...
This is totally separate topic and probably a lot more work and it is better to discuss it later, when the cpu registers problem is solved.
The problems with interfacing with the debugger from another plugin is that:
1. parsing the output is hard and is done on per command basis, so you need to do some parsing in your plugin.
2. you make a connection where your plugin starts to depend on the behaviour of one particular debugger plugin, which is not a good idea.
Sad... i think there would be a lot potential. Specially in automation of gdb things and embedded stuff (see previous image)...
Now we have python printers directly in gdb, which do better job handling the watches. Our scripts for the watches need lots of work, I'm not sure how to do even. We need a way to execute a command, wait for its output, parse it, execute another command and so on.
If you have idea where scripting might help, I'm ready to discuss them.