Oh yeah, I've done pretty well in preparing myself vs. D3. It's really all a guessing game when you are putting high pressure, except a wrong guess could get you like 35%. One thing I like to do sometimes is SH fair -> retreating AS as I land, they get so greedy to grab they usually don't see AS coming and if they shield it allows some time to reset or try for pressure. Also crossups seem pretty good (SH fair -> landing on the other side then grabbing/jabbing).
I've found the Close Combat stuff seems to have some potential against him, mainly because his DI/aerial movement stinks if you get him with jabs.
marth on the other hand, seems pretty hard, I don't have anyone I play actively in my region, but taking from my experience as an ex-marth, it's pretty tough.