Sure why not. I very much doubt at almost 40 she would beat the Williams on a fast court, even in their current shape. Actually at almost 40 she might have a shot vs Venus on rebound ace or clay, or Serena on clay, the way the sisters play those surfaces these days which is pretty sad. However at Wimbledon the others outside the past their prime but still unbeatable on grass Williams are so hopeless that returning as a 40 year old trained hard and ready she might have a shot vs anyone else if she avoided the Williams. A healthy Sharapova would also take her I am pretty sure, but how often do we see that these days. Against a 40 year old fully trained Graf players like Kuznetsova, Safina, Dementieva, despite grass being their worst surface might take a huge lead on Graf if they played at Wimbledon but then might self destruct with a horde of errors and double faults allowing Graf to make a big comeback and win. Well maybe Kuznetsova will change her stripes after this years French, who knows. Ivanovic and Jankovic a 40 year old Graf probably wouldnt need the assistance on grass.
Anyway regarding Date she played very well in the exhibitions last year. She beat both Graf and Navratilova in her matches. Navratilova is over a decade older than both but has also been playing alot more serious tennis than both this decade. Date and Graf are almost the same age, Date had probably been training and getting in shape for her comeback anyway though. I always like her. I would like to see her win some matches at Wimbledon. Given the current weak womens field you never know. If she gets a good draw she could maybe win some matches and that would be a good achievment for her. She was probably robbed at Wimbledon 96 where they should have finished play that day. That isnt Graf's fault though, The All England Club always gives champions the benefit of doubt though.