To add a new measures group for Nutrition data, similar to current Body/Hrv would be relatively straightforward and daily energy balance could be computed in R/Python charts using existing Measures APIs, but not via Metrics Trends chart formulas since they are computed per activity instead of per day.
OTOH the ability to add custom measures would be interesting since people may like to register sleep data, laboratory measures or just subjective well being information, but this would require some re-design and further restructuring the code.