You have an idea, you have some skills to realize your idea. You should be able to make some money off that idea. That's the theory and practice in Arduino DIY for a while but I know that many are angered by all the cheap modules and arduino clones on ebay and beyond. There seems to be nothing you can design to have any price advantage over the flood of modules when a module is sold cheaper with free shipping on ebay than the key component featured on the module. Say I design a board featuring ATMEGA328P. The 328P is about $4 each. Then a nano clone costs only $3 -$3.50 so why designing anything?!
That was my opinion for a while.