When typing in /gamerule dod It will not autocomplete to /gamerule doDaylightCycle, but it must be /gamerule doD before it autocompletes to /gamerule doDaylightCycle

This may be intentional, as the new command system is supposed to be case-sensitive. However, tab-completion is supposed to speed things up and help you find what you're looking for, and it would be nice if you could successfully autocomplete without worrying whether you typed in correct capitalization or not.