We would love GParted to support LVM2 Volume Groups and Logical Volumes. (It already supports Physical Volumes).
We wish to encourage contributions and to ensure that all time and efforts are well spent. To help in this regard we highly recommend proceeding in small steps to ensure that changes are aligned with the user interface, match with existing code design, and enable future code maintainability. This helps us to better understand each other and hopefully avoid lost productivity.
What follows is just some caution and not trying to stop you doing this. We have had previous cases of people coming in and trying to change a lot of code before. They have ended when the developer lost enthusiasm and the code not being in a fit state to accept. Also note that everyone works on the GParted project as a free time hobby.
I think what you are suggesting will be a bigger task than you think. I wouldn't be surprised for what you have outlined to take changing (adding, removing and updating) 2000 to 5000 lines. For reference when I was just adding LVM2 PV support I changed over 1700 lines in 33 commits and the work spanned over six months:
Please note that we need a coherent UI which is easy to understand and in keeping with how GParted already works. We also need well structured, maintainable code.
So if you are committed to doing this we suggest producing a design for how the UI will work. Even just ascii text pictures and some description will do. We (GParted Developers) will review it and we'll go from there.