Should rice be started in cold or boiling water?
It doesn't make much difference. A few things to consider and also why I use cold water.


Once you bring the water to a boil you need to turn  it down to a simmer. Adding cold rice at this point can thriw off this process.
Rice is typically cooked based on ratios of volume. Boiling the water first won't effect this unless you lose track of it and the boiling causes your water content to reduce.
Lastly rice cookers these days are set-and-forget and boiling the water first is an unnecessary step.


All in all boiling your water first is not a problem but doesn't add any value.