Hussar - "Perhaps tying the paladin with a Holy Weapon might be a good idea. That's at least distinct from other warrior classes. Sort of like the Kensai from Oriental Adventures. Bit weak, IMO, but, at least it's distinct."
Love that idea (can't XP you)
A morning "bless my rifle"-type ritual could make this sword, or mace, or axe, your current Holy Weapon, which gives a persistent +1 / holy property (unholy for anti-paladins, one would presume). If you lose your weapon or it breaks you can re-bless another one tomorrow and keep on.
At higher levels that blessing gives greater benefits. A fighter gets a +1 period, but a paladin gets it on his "Holy Avenger"-esque weapon. Of course, I don't know if this should stack with the holy avenger weapon type, I would say Yes...but "smite evil" and undead killing should definitely be part of the class.
Also, a paladin would be particularly good at not getting killed by specifically evil-aura creatures such as undead and ghosts and vampires and demons...Are those not good enough "class-defining" features? I fail to see how it would be feasible to add those types of buffs via a few feats on top of a generic fighter in plate with LG or LE alignment background. If undead-crusader is a feat available to all followers of an LG god...then maybe a theme would make paladinhood doable. But that's a non-starter because it will be a class.
I'd much rather be able to play a paladin, and THEN take a theme that makes me super good on horses, or be able to dual wield longswords or bastard swords or one longsword and one battleaxe or a battleaxe and a warhammer.
Think Optimus Prime in the third movie there, when he's dual-wielding the sword + axe combo and kicks ass all over the battlefield FTW. You can't have your class features as a "theme" and still allow for "leader" or "dual wielder".
You NEED to have "defend the weak, protect the innocent" type abilities by default. You are a defender, who epitomizes the "holy avenger" archetype. It's not just a weapon, it's he/she who wields it that is the true Avenger.