You could in fact have such a familiar. You just wouldn't be able to polymorph into one. Like lets say its a Nosoi or a Shinkigami. Not once in the actual text does it state your familiar must be an animal for the Beast-Bonded archetype, just that you do in fact have a familiar for stuff like the cheeseball glory known as Twin Soul.
Enhanced Familiar will make it so if you crossclass as a witch your familiar is still pretty potent. Plus if you wanted to you could always throw in the Boon Companion feat so that your familiar always is treated effectively as +5 levels higher than it actually is (I.E: Four levels in witch and four in X + beast-bonded + boon companion = Level 9 Familiar even though you yourself are only effectively a level 4 witch)