Theorizing: what can be done with DOT clock signal present on C64 expansion port?

Ideas:

- Create a secondary display card with a VIC-II that would use
   its own memory.

- Create a secondary sound card that would play digital sound
   alongside the SID.

- Create a math coprocessor that would accelerate programs or games
   that use intensive number crunching.


...all of it in sync with the rest of the system.

What do you think?