OK… I know that 1000 is mentioned in Ws2801 and know people that have built to this limit . but always thought ws2811 was limitless theoretically. Wish I had enough LEDs to visualize the delay that would inherently occur with the propagation of that signal?
“Limitless” is relative and to a point … consider RAM usage, consider the time it takes to go from px0 to px999 … the time it takes to update all of it will determine how “limitless” you want to go.
@Justin_Eastman , crazy idea but it also got me thinking what it would look like… 
Starting with a Teensy3.1 with 64Kb of ram, that would physically allow about 21,000 WS2812 devices and the extra 1Kb ram is probably ok for loading the FastLED library and run the very simplest of sketch.
If you used qty 144 of the 144LED/Meter strips that gives you 20,736 ws2812 LEDS. I will totally ignore the details of power distribution for now.
I would tightly stack the strips side by side such that I get 1 meter X 1.72 meter (144 X 12mm wide) 2D array.
Not considering the potential for parallel output on the Teensy3.1 I would connect all the strips in series and connect that to a single pin of the Teensy3.1.
20,736 X 30uSec = 0.62 Seconds !!!
So if my sketch consists of a simple blinking from red to green to blue of all the LEDs without any other delay, the panel would take 0.62 seconds to draw all red and 0.62 seconds to draw all green etc… etc…
That is almost 2 frames per second, still impressive !!