Hello, IMHO it needs a 3nd date-mode. I use deadline for all thinks that have to be done until the deadline-date. I use scheduled for a fix date ...
and what about thinks that could start at a date "or later". I tried to fix it by using a time for fix and no time for non-fixed or has-to-be-start dates, but this is no solution, because there are todos that have to be done on a fix-time and others only on a fix day. But never the less I use a lot of planning tools but org-mode fits best for all my needs - thanks - Michael