I would like to see more frontends as well done and user friendly as DVD-toys.
An SVCD & DVD authoring program is high on my list. There are several frontends today, like CD-Burn, DVD-burn, Q-DVD (port of Paul S), and Varsha (java), but I've in fact never suceeded in building and/or burning an SVCD or DVD with any of them. Though there are some help to configure it is just too hard for an enduser.
In a GUI I think the software must have the possibility to handle the process the whole way from "any" file (that ffmpeg can handle) to a ready SVCD. You should have easy choices like "Make SVCD" or "Make DVD" or "Fit files to medium". With the last option I intend that the program calculates best possible quality to chosen media (CD or DVD), which will give you the whole mediastream on one CD or one DVD with best possible quality.