I actually really like the idea of Albus being a Slytherin, and James and Lily being Gryffindors. It would make for some fun family rivalry in Quidditch season (especially if Albus inherits Harry's Quidditch talent as well as his looks). Also JK has said that Slytherin is changing and losing its dark reputation, and a Potter/Weasley entering that house (and maybe befriending a Malfoy?) could be part of that.
Wow, long post! Sorry. Anyway I'm really enjoying looking through your art today.