Other than chain length, what are the limitations to the number of gear teeth?
In the diagram below (from Park Tool) one can notice that if the innermost (lowest) cog grows much larger it will interfere with the top pulley on the rear derailleur. This is the primary limiting factor for the size of cogs.

(source: parktool.com)
For chainwheels, I suspect that the ground would be the physical limit (for a typical diamond frame, anyway).  Of course you'd better eat a good breakfast and have a friend with a shed on his car if you plan to turn a ring that big.