Just a minor update - I have done some 'simplification': halved the instruction set to 8 instructions total, and reduced the ALU to 4 functions. This will allow a significant reduction in the amount of hardware I'll need to make, while still allowing meaningful programs to be written. I'm also taking some inspiration from the Kenbak-1 - the I/O has been reduced to one input and one output port of 8 bits each. If this seems extreme, recall that the T-1 is more or less an 'art project' - I'm not trying to replace a desktop PC.
And there's always I2C/SPI :)