Hmm, if the prerequisite for the Phylactery would change to:
"Only creatures with a caster level 11 or higer in an arcane or divine spellcasting class can create it.
Druids that willingly become undead do violate the Druid`s Oath and would lose all spellcasting ability, before they even could finish the Phylactery. Paladins or Ranger`s usually can`t reach the caster level requirement, and Paladins would violate their code of conduct creating a phylactery, even if they ever reach that level ...",
there would be no problem for a Bard Lich, except the usual "doing evil deeds to get it"
I think the character (be it a NPC or PC) is valid, and since rules shouldn`t limit your imagination...
This reminds me of one of the adventures I wrote and mastered - a Dwarfen Bard was victim of a genetic disease (it`s a dragonstar based world), that would kill him in a few years (slowly reducing his con...), and he searched for a way out of this - He know he wasn`t strong enough to become a lich (besides the fact that he was a Bard, not Cleric, Sorceror or Wizard), but he heard that many heros that were killed by true Vampires could become a true Vampire as well, not only Vampire Spawn, keeping most of their personality and character. So he searched for some real Vampires, that would kill him to reach his eternal life.
He left his "true love" to search for Vampires - he catpured some younger people and offered them to some vampires, so they would "sire" him...
The characters appeared on the scence after this happened, and got onto the trail of the happenings (while they were searching for a completely other person)
The Bard and the Vampire were going to leave, but he wanted to return to his "true love" and take her with him, possibly "vampify" her as well...
Mustrum Ridcully