> ...it would likely be slow and limited to text only. The system bus or > parallel port would be MUCH faster for this...
Well, there are SPI BT/BLE modules so speed to the ModelT side shouldn't be too bad, either using the bus or the parallel port... Alternatively, there are modules like this (VGA colour display and FAT-compatible SD card storage): https://www.4dsystems.com.au/product/uVGA_III/ Of course before long you'd have lots of stuff hanging off the ModelT again... FWIW, here's what an M100 in 80x24 mode looks like (can't find a picture of 8x40 on a big screen TV at the moment):
