The 721 will get 600mm right on the end of the cut, I have steel box section fences with a flip stop system so i set them back just a bit further, Where i used to work you had to lift the board up just to cut the last little bit, Not good really.
There is a router attachment available, I did look ages ago but you have to remove the guard and blade as it seems to fit the arbour if i remember right.
As for trenching, The flange on the saw needs to be machined to take the thicker blade, I had to do this on the 728 3 phase i have just for trenching.
Youll need to remove the riving knife from the guard too. Those Freud Dado cutters from machine mart work ok, I dont like all the bits you sandwich together, You cant beat a nice replaceable tip Garniga one, But theyre a fortune (and about 2 month wait!).