The theme that would suit a contemporary Romeo and Juliet would be an Urban theme, one that is set in somewhere such as East London and the Capulet's and the Montague's could or should be families that live at either end of the counsel estate and possibly they could be the two families to know around the estate.

Though the Shakespearean English should still be used but the accents should be extremely contemporary and rather urban. The two families should have their own style and their own eccentricities such as one family could possibly have a south London accent and the other could have an east London accent.

Possibly the race issue could be employed as one family could be black and the other family could be white and the fact that the Capulets white daughter is in love with the Montague's black son could cause...