I often use more that 1 USART and 8 analog input Hence usability. The drawback i see in my design is the 12MHz clock, a bit on the slow side.
And yes, one of the ideas was to make the system robust Both the lab module and the application modules are self contained. I have been doing a number of designs with the Nano/Micro/Mini style arduinos on breadboard style pcb's. It's a quick and convenient way to work. Lately i have been using Tiny 84 in dip packages directly on those boards.
So the design is more a development of that (with the addition of a power supply) than trying to replace a mega 328.
The idea was once the design is finalized and the components are soldered onto the application module (only one pcb with CPU, LDO and application specific components) the lab module is free for the next project.
What im thinking of is adding some SOIC prototype area so you can use these directly since DIP's are getting more and more scarce and i want to get away from modules and breakout boards since they increase cost and decrease robustness.
Im attaching a image of the application module PCB
