@Crake so the text is thus:
Wild Arcana (Su): As a
swift standard action, you can expend one use of mythic power to cast
any one arcane spell without expending a prepared spell or spell slot. The spell
must be on one of your arcane class spell lists and must be of a level that you can cast with that arcane spellcasting class. You don't need to have the spell prepared, nor does it need to be on your list of spells known. When casting a spell in this way, you treat your caster level as 2 levels higher for the purpose of any effect dependent on level. You can apply any metamagic feats you know to this spell, but its total adjusted level can't be greater than that of the highest-level arcane spell you can cast from that spellcasting class
Our spell list is Sorcerer
and Cleric, and we always cast spells we know from the latter as arcane, so as far as I would rule it, yeah.
If a sorcerer can pick spells known on from the sorcerer and cleric lists, isn't the sum of those his "class spell list"? I'm given to understand the various ACFs and feats and classes which modify one's spell list would make those extra spells eligible for such an ability. That the modification was "add the entire cleric list, and these domains" shouldn't change that.
@DragonParadox ?