Looks good! I have a AdaFruit LCD that uses the MCP23017. I can’t test it right away but will give it a try. It appears that I can define the MCP23017 and it should work? The use of the small adapter board with pull ups isn’t clear to me – when is that to be used?
You say “temporary” and I am noticing this idea has been kicking around for over two years. Might be one of those permanent temporary things… 🙂