To summarize I think:
You want a setting in the General section of Kagi (makes sense next to the temperature and time settings) for measurements system (imperial/metric).
This could be used in various ways, including but not limited to:
If Quick Answer replies, it would reply in your preferred units (metric/imperial)
(this one is probably more complicated and note sure what the best approach here would be) is that you requested to have the whole site you visit show the correct measurement units.. which would almost require a kagi translate level thing that parses the website but only detects the units and changes those. Which is possible but yeah...
UPDATE: so Quick Answer already takes region into account, so it already converts to your normal units. But still, if your units don't match, could be interesting to manually set them i guess
Also actually: this could be useful for Kagi maps to use as well, now that I think about it