The best choice for our Mythic feat is definitely the Extra Path ability. Beyond Morality isn't my favorite option. It's super niche for what it actually does, but what it does just happens to provide a very significant defense against a certain class of spells that is almost impossible to come by in any other form, especially such an absolute counter. I won't argue if ya'll want to go with Beyond Morality.
The only other Mythic feat option worth considering, IMO, is one
@TalonofAnathrax also brought up, Mythic Paragon. That one would do some good things for Viserys, including increasing his Initiative by another +2, raising his resting caster level for Fire spells to 29th, expanding the range of Divine Source spells available to any Clerics who might reach that level of power, opens up the 6th and 7th level spells and SLAs for us from Divine Source, etc.
We've been using Wild Arcana to duplicate Spellbane as needed since the day we gained the ability to cast 9th level spells. It's not been an issue up until now that we didn't actually know it. I wouldn't be opposed to learning it for real when the opportunity presents itself.