I thought the special features were good, but new ones would be a bonus for sure. Commentaries with some key cast/crew members, retrospective interviews, deleted scenes, never before released behind-the-scenes footage, etc. in addition to the features on the DVDs would be nice.
The only reason the T-Rex lost in JP3 period was because of Jack Horner with his stupid anti-Tyrannosaurus agenda he finally got around to infusing the movie with at the time. His theories on the T-Rex being a scavenger have been disproven and IIRC, he even admitted later on his theories were wrong.