I have a small feature idea, that could actually be implemented rather easily I believe, since a lot of the code to do it is already under the GPL.
The idea is to allow the user to select from multiple scaling algorithms, Advanced MAME2X and the various 2xSaI algorithms http://bob.allegronetwork.com/projects.html and http://en.wikipedia.org/wiki/2xSaI.
These algorithms would be very useful for antialiasing purposes, as of course turning on antialiasing on the main machine that is being used is rather pointless (well except for slowing things down, I noticed that with all VNC viewer applications!), and for the most part the computer screen consists of well defined shapes and such, making 2xSaI a potentially good fit for a scaling algorithm.
http://scale2x.sourceforge.net/ (Advanced MAME 2x) is GPL as well.
I do not know how applicable the various hqnx algorithms are for arbitrary scaling amounts, but who knows, maybe an image could be scaled up 2x and then dropped down to the desired size, with a better effect than just scaling up? It is not like there isn't CPU power.

And a link to hqnx pages:
http://www.hiend3d.com/hq2x.html[/i]