Ok, André, I've done as you desired and stripped out all the InsetGraphics nonsense from the graphics cache. InsetGraphics now has code to generate the pixmap once the file is loaded.
LyXScreen (frontends/screen.C) has some equivalent code so that we can show the splash screen once again. So, we have a flexible image loader but I'm not so sure that code re-use is optimal yet ;-) Anyway, it's a start. Best regards, Angus