Hmm ... if we have good LUA-scripting with many events, actions etc. we would just need the possibility of adding Triggers to units - which would be good too for several things like Units becoming "smaller" units when they die, units which double after some attacks etc.
If we had this, and I think this is not a very low priority topic, adding these features would be really easy because you could just add the event "Sunrise" to every unit and issue the morph/disappear etc. functions there - this leads to another important (optimization) thing: It is IMHO necessary to union Triggers for shared events to not let so much events get called at sunrise (Maybe this is already implemented, I still haven't read the source code really :-( ).