Please note that the option is available on the windows client through the switchboard. When you see an incoming call in the switchboard you can right click on it and use the diversion option.
You can also post this as an idea on https://www.3cx.com/community/forums/3cx-ideas/ . All posts are reviewed by their corresponding Departments and, if feasible and voted for by other users as well, may be implemented in an upcoming service pack or update.