Part of the reasons for notify-osd is a very elegant and universal notification system. As far as I know, the theme is built into the code and would require a complete rewrite to allow this.
If you want a different theme, you could "apt-get source notify-osd" and change it yourself.
The current notification looks great. Bringing this theme feature should not affect the performance of the app. If it does then I am against it.Just my opinion
Saying that unhappy users should just change it themselves is a cop out.*
If the average user wants to customize the notification system's behavior, are they going to hack the existing system or replace it with an alternative system? I don't think so.
There are legitimate reasons for not letting the user customize the notification system (e.g., feature bloat, option bloat, lack of simplicity/universality). Issues like these are the ones that should be addressed.
*That may be a bit strong, and I don't mean it offensively. But it had to be said.
It's a design decision to specifically not allow the notifications to be themable. I don't know what reason the Canonical devs have for this, but it seems a very weird position to take.
The specifications for Notify OSD state:
"Regardless of type, a bubble should appear as a rectangle of color #131313 (regardless of theme) with opacity 90%, corner roundness 0.375 em, and a drop shadow of #000000 color and 0.5 em spread. The bubble should blur whatever is behind it with a Gaussian blur of 0.125 em."
I don't don't it should be via gconf-editor. Gconf editor should only be used to access advanced settings. This pretty basic, and pretty much EVERY implementation of this allows theming
Despite your wishes, Andrew, gconf-editor isn't used for settings much more advanced than can be configured with existing guis. It's a little hard to learn where things are, but it's really easy to use. You should actually try it before judging it.
This type of feature creep would lead us down a path I don't want to go down. Soon enough Ubuntu would start being as cluttered as KDE.
As for "EVERY" implementation of this allowing theming, "notify-osd theme" is not a very fruitful google search.
I have tried it in the past. Its pretty much just a clone of regedit. However, its odd that you are suggesting that people should use it..
What do you mean by feature creep though? And where do you draw the line? You can make an OS damned advanced without cluttering the gui. Look at Maya for instance.
I don't think people should need to touch gconf editor at all