I, personally, think it would be really neat to see a rival-centric GBC mod. And if you have the skill to pull a full-length game off(and what do I know, perhaps you do!), then it would be awesome to have another full Pokémon Gold hack to play besides the upcoming Pokémon Prism.
It turns out that, even though the last demo was 2 and a half years ago(oh the irony), <em class='bbc'>he's been working on Prism this whole time.</em>
There are updates on the Facebook page, and he's said that the Final will be released sometime this year!
Go for it! <img src='http://www.cavestory.org/forums/public/style_emoticons/<#EMO_DIR#>/chin.gif' class='bbc_emoticon' alt=':chin:' />