this would be a great move, but what make you think the Mavs would agree. They will probably shop Finley and Walker this summer, but why would they want an aging SG, that wouldn't fit into the Mavs run-n-gun style at all. I hope the Knicks can find a taker for Houston, but I don't think it will be the Mavs.
I know they are interested in Kurt Thomas for defensive purposes, but that wouldn't be enough reason to take on Houston.
For the Knicks though this would be a good trade. They get rid of an aging, deteriorating SG for a younger SG that has a game that slightly resembles that of a younger Houston.
Also, the Mavs don't have a 1st round pick this year to trade, so it would have to be a future pick.