Jim
Yes I suppose there could be something on our base Flight Planning system, however that would only cater for takeoffs from Base. Takeoffs from offshore back to base, or to an alternate could not be covered since surface temperature and pressure are not forecast in TAFs etc. (I am discounting density altitude offshore since it never gets that cold)
I suggest that (just like EGPWS obstacle data) its better to have no electronic system than one that only covers half our flight sectors. That way the pilot is in no doubt that he is responsible for compliance with flight envelope limits. Not all operators have electronic flight despatch systems anyway.
One of our complaints about this limit (which you may remember was introduced a couple of years after we started operating the aircraft) is that its not really possible for the pilot to predict the density altitude at his destination at the end of a long flight. Experience and good judgement are the only weapons available. If you don't like the sound of that you are not alone, but what is the alternative?
HC