I did something similar about a year ago: 
There didn't seem to be a lot of interest in the board though so I never sold any. I'm curious how your kit will do.
I'm wondering though why you used the TLC5490 chips. At $8 each (from seeedstudio), that would be $24 of the $35 price tag. My design uses 11 Arduino lines to control the LEDs (for your 16 LEDs, I'd need 14 lines). I have interrupt-timer based firmware so controlling the LEDs is similar to how you described yours.
If you don't want to tie up 14 lines and do the work in software, why not put a daughter ATmega on the shield? A $4 ATmega plus 6 transistors vs $24 in driver chips seems like an easy choice. You could knock it from $35 down to $20 and still make more off each one.