nope, but I implemented something similar but never published it due to several factors (which all lead to the issue they are fixing in the core).
1) RMT needs to be useable by more than one library, and currently they way its implemented it can not be. It has 8 channels that can be used.
2) The current ISR requires the data be in a format that requires 32 bits to represent 1 NeoPixel bit. So a single pixel would require at least 96 bytes to represent. This blows available RAM very quickly for any larger collections of NeoPixels.