Sounds like a great interface. Would it really be that cheap to add I2C to a shield?
I recently saw an I2C LED going for like $12.95 a very nice LED, but say the LED was worth .50c thats $12.45 for the rest(I2Cand a tiny board)
The LED looked something like this
http://search.ebay.com/search/search.dll?query=50-PC-5mm-8Kmcd-Common-Cathode-Super-Flux-RGB-LED&MfcISAPICommand=GetResult&ht=1&ebaytag1=ebayreg&srchdesc=n&maxRecordsReturned=300&maxRecordsPerPage=50&SortProperty=MetaEndSort
I'm sure if quantity they would be cheaper.