While a GUI wrapper on top of gdb can be easier to use for some things, I wouldn't call commandline gdb hard to use.
If you have gdb working why can't you get ddd or eclipse working on top of it?
ddd is available in the debian repos so you can just install it on OS's like linux mint.
In the bigger picture, source level debugging being integrated into the IDE would seem to go against the current views of some of the core Arduino Team members that seem to be dead set against doing anything that they call "advanced" for fear of scaring
their less technical users.
I mean I got extreme push back from them for simply trying to get printf() added to the Print class.
Source level debugging is a much higher technical bar than a simple print formatting routine and I would think that those that were opposed to adding printf() to the Print class would not be in favor of adding source level debugging to the IDE.
My view is that anybody that wants to do advanced coding and debugging should probably look elsewhere than the IDE anyway.
For those that are using operating systems designed for s/w development, like *nix machines, the tools already exist to do source level debugging.
The trick is to learn what they are how to set up your environment to use them.
--- bill