Thanks! The board does have a serial port, but it is not RS-232 voltage level compliant. An external level converter could be added. It would be easy to write a DSR extension to support the serial port from Basic. It is not hardware compatible with the TMS9902, though. If I implement a follow up board to this one at some point with an actual FPGA we could have hardware compatibility. Anyway for my purposes the USB port is hugely more useful, and a whole lot faster.
I personally no longer use my RS232 card, but I know a lot of other guys who do.
I think the primary goal of this card though is to provide a full disk and memory system for a standard TI console. The fact my game will be playable on it is a HUGE deal to me!