Weakest link in lifetime of electronic circuits
There are standardized methods for calculating reliability such as Bellcore Telcordia. Accuracy may be questioned, but they provide a basis for comparison. 

I don't imagine there is any need for electrolytic capacitors in an SBC, as the power supply would likely best be separate, and there is little need for tantalum parts with the progress in MLCC caps.

Complex things like memory chips running very hot, and large numbers of MLCC bypass caps should probably figure into your lifetime calculations. Relays have a defined life, optoelectronics generally ages, but VLSI chips also have a temperature-dependent lifetime due to some mechanisms like metal migration. MLCCs can fail shorted. 

And, if you're not selling a packaged bulletproof product, the lifetime may be foreshortened by user activities. I once received a "warranty repair" temperature controller that had failed due to a forklift tine penetrating the front panel to a depth of at least 6". They'll do stuff like connect 240VAC to ADC inputs and put electronics in lightning-prone locations.