What do you want to achieve by thos crossing? What conception do you have?
It's the first question all breeders have to ask from herself when crossing two purebreds from different breds.
These two horses stand very-very far from each other. Why do you want to cross an athletic, thin, respiratoric, impulsive horse with a calm, cold-blooded fashion draft horse? To have an average riding horse with a good shape? Then buy a beautiful hannoverian, holsteiner or a Dutch warmblood or something else. As much as I know, friesans are good only for hobby. They cannot jump, they don't have any prominent sport performance, they can be trained for show riding... as much as any other breed. And I can tell you that none of them are as good in cart driving as a Nonius or a Lipizzian or a trotter cross.
The same is true about arabians: they are good only for hobby or endurance riding.
By the other hand, if I wanted a horse looking like an arabian, I would buy an arabian. If I wanted a horse looking like a friesan, I would like to buy a friesan.
It's a good idea to cross them if you want a beautyful, black horse for yourself but I'm afraid no one will buy any of these crosses.
I agree with JustDressageIt, these cross appears to have no sense to me, but I'm opened for conviction.