The placeholder Monkey Island graphics will soon be replaced. In a way this is a shame as they're obviously of professional quality and gave the XAGE youtube videos an extra layer of polish.
I'd expected that I'd need to replace them with either some suitable public domain graphics (none of which I was able to find) or to approach an AGS developer to use theirs. In fact the answer had been staring me in the face all along. In the mid-90's an elder brother and I had spent countless months of our misspent youth making simple adventure games with AMOS for the Amiga 500. It transpires that my brother had actually recently managed to convert a bunch of our (mostly his, my creativity has always been highly derivative) deluxe paint drawings of various characters and locations. At some point Guybrush and the Governer's Mansion will be replaced with Artichoke and the island of Uh-Oh Yeti:
Also, I've contacted the creator of an AGS game who is potentially interested in converting his game to XAGE for release on the Xbox360. Nothing is set in stone yet but this is a particularly exciting development and can only make XAGE more robust as I implement all the functionality I've overlooked as part of the conversion progress. It should also be possible to automate parts of the conversion, specifically dialogue trees.