Elles and others - why do you keep mentioning TBs from past decades that were used for sporthorse breeding?
Do you not understand that today’s TB, and today’s WB are different animals than in the 60’s, 70’s, 80’s, even the 90’s? 
Today’s dressage and showjumping bred WB so far outstrips today’s TB in terms of sporthorse qualities (esp. at the top levels), that adding blood from today’s TB, is - as Bayhawk and others keeping pointing out - going to very, very likely be detrimental to the WB, particularly in the F1 generation. The breeders in Europe know it, and savvy breeders in NA and elsewhere know it, which is why most of them say, “Yeah, let my neighbor do it.” If they need “blood”, they go to another population such as SF, that has been specifically developed for sport horse qualities.
But I suppose a handful of TB fanatics on this forum know SO MUCH MORE about sporthorse breeding than those folks in Germany and Holland, etc., who have seen hundreds upon hundreds upon hundreds of foals grow up and move into sport (or not). :rolleyes:
And because I just know some of you are going to get on a tangent about event horses, let me state right here and now that my comments above pertain specifically to the disciplines of dressage and show jumping. Breeding for event horses is another beast entirely.