You can do a lot of libraries mainly in hardware such as Wire (i2c), SPI, Serial (uart), and you can do some parts of gpio, PWM and other core functions in hardware. How you do USB and analog input is probably dependent on the board, and ADC might need addon hardware.
I don't think the fact that Arduino have done this badly and with closed source for Vidor invalidates the concept. An Arduino device with as many hardware i2c, SPI, uart and PWM pins as you want seems useful to me. And it will drive a lot of other hardware much better than a microcontroller, such as LED panels and strips, VGA, HDMI etc.
And this would be just one way to use my* or BlackEdge.