Anybody know how many programmable RBG Neopixel strings can be driven in parallel from a single Arduino Mega output pin. I am not asking how many in series can be driven. That is unlimited if you provide the required power at appropriate locations along the length of the string. I understand that each of the Neopixels at the same position on the parallel strings of would have the same "address". That is acceptable for my application. I just want to know how many parallel strings can start from a single output pin without damaging the Mega by drawing too much current or having the available current too low to drive all of the parallel Neopixels.
About 20 after that you need a buffer. The proper name for your question is called the fanout of you device.
Use an external 5V supply, not the Mega supply. If you buffer the signal as Grumpy Mike suggests, the amount you can have in parallel is effectively limitless.
I have a project that has 45 shift registers - SCK and SS are buffered and go to all of them parallel, while MOSI s daicychained from part to part. That runs with SCK at 8 MHz. Neopixel runs at 1/10th to 1/20th of that speed.