Actually all the orignal holy avengers were the same, exactly same powers and all were long swordsloot is not a way to help the paladin class in any case but this (exclusive to paladin item) case
in any case, as we all know, not all holy avengers were really created alike, and most had unique names and powers (the dispel and sr abilities werent even universal, though close).
there were extra damage vs chaotic evil avengers, extra damage vs evil spellcaster avengers, etc, etc
there's no reason not to have some customizability (hell, just a series of choices that leads to 4-5 template avengers with unique names would rock) in an item that if designed well should be part and parcel of every paladin build.
if this item is a longsword, my paladin will not use it, and that will disappoint me enormously.
if it isn't keen, im gonna have a hard time working it in as it is (a rapier variant may be an option, but i'd rather have a keen slashing avenger), and Im already turning tricks trying to figure out if it will have an insight ac option (a big problem for me as well, though one i can manage around by doing triple leviks)
another idea:
this item should have 3 unlockable powers entirely separate from any choices, level options, etc:
it should gain 1 different power for each of the paladin prestige classes (scaling up the bonus for the class tiers: having defender of siberys I gives you a certain bonus (even if you have 20 pally levels, you may for some reason choose not to do all 3 tiers of an enhancement), having defender of sib 3 = bigger bonus of the same type).
no one can have more than one anyway, but this would be a really cool way to further synergize the avenger with the prcs, and they've already said that mod9 raidloot will have effects that synergize with capstone enhancements, so they are already designing this mechanic.