The problem is that you can't just insert a higher res image and expect the engine to render it correctly.
But fear not, this is on my to-do list for the OpenGL driver, I have already experimented with extracting the different layers of backgrounds etc., I just have to come up with a good checksum/replacement system.
It's not going to happen with the next version, and probably not even in the version after that, but it will be there eventually.