That's a lot of good info, CrossRoads.
I'm thinking it may be possible to simplify life by using an MCP2221. I'm digging into that more as we speak. It seems to be similar to the FT232H in that it offers I2C or SPI, but it seems that support for that is baked into their drivers.
pito, thanks, man! This info has given me more excitement. I was getting bummed about coming up with a USB solution.