The 16U2 on my UNO-R3

I vaguely remember once in my early research on the Arduino that you can reprogram the 16U2 that is on there as the Serial to USB bridge.

I wonder if that chip has any resources available to us?

What pins from it are actually connected to Arduino? I assume that none of the digital IO pins are available, but do I get anything more than the two Serial lines and a reset?

How much of the memory on that chip is being used? How about the EEPROM on it?

I am wondering if the code on the 16U2 could be updated with an escape sequence that lets me take it out of USB mode and talk to it directly. If there is a substantial amount of code space over there it could be used to store tables of constants or other such data. If nothing else it might be useful to be able to send an escape sequence and an address to get an extra 0.5K of EEPROM.

I don't know if it would be useful or not, but I was considering the 16U2 alone for another project and while I was reading the datasheet it dawned on me that we really aren't using much of that chip on the Arduino and wondered if there were any resources to scavenge.

For the complexity this would involve, I think it would be simpler to upgrade to a larger chip, for example the Atmega1284P has 16 kB of RAM and 128 kB of program memory. That is obtainable in a DIP configuration.