|Not all paladins ride horses or wield swords.|
At the concept level I would wonder what actually makes a cleric and paladin distinct. Both are holy warriors that wear heavy armor, attack things in melee, and can cast divine spells. Going to the mechanical level using that mission statement, I guess you could just combine some elements of the cleric and fighter to make a new class...but then why not just let players use the 3rd Edition multiclass method that it sounds like 5th Edition will use to do it themselves?
3rd Edition gave the paladin exclusive class features like detect evil, smite evil, immunity to fear and diseases, the ability to summon a celestial horse, Lawful Stupid jokes...things that you could not get no matter how you tried to mix and match the fighter and cleric. 4th Edition made it possible to blur the line between a cleric and paladin by taking the right feats and prayers, though clerics still got turn undead, encounter-based healing, and at-will ranged attacks, while paladins were more melee focused, and got Divine Challenge and lay on hands.
To me it is not about mixing and matching until you get an iconic result. I want the paladin--or any class for that matter--to provide features and options that you cannot get just by mashing two other classes together. That just sounds lazy. I am hoping that the designers at least give us iconic paladin stuff that we have seen before; even a rehash sounds better than something that anyone could have just done themselves.
What sort of class features do you think a paladin needs to be a paladin?