I think @danielt already explained a work around for add 5v or 3v3 devices to the db410c gpio. AFAIK 1v8 was decided as the voltage for two main reasons:
1) Most SoC default to 1v8 on the gpio and it reduces complexity while designing a dev board.
2) Most sensors available in the market and the ones that are there on smartphone are also 1v8. Arduino and Rpi compatible sensor modules available online just have level snifters on board to make them compatible with 5v and 3v3.
So at the end if we had 3v3 or 5v on LS we would simply end up level shifting twice.
Also this makes it easier for people who design mezzanines (add on boards) for out devices as they don't have to level-shift and can directly add sensors to their designs.