Yeah I miss the paladin. Hope he returns in an expansion.
Not gonna happen.
Monk has Mantra's which are basically slightly more well balanced Aura's and an array of holy type spells with some similarities to the Paladins skills. Theres simply no room for him.
They will probably add another melee class at some point, to make a 2nd Strength based hero. All I can really think of in that respect is something resembling the Druid with Shapeshifting and Beast mastery.