That was my biggest issue with spell versatility if you read it as making the favored soul spells count as arcane 24h then you could argue that the favored soul spells are arcane, and from there there would only be a step to: favored soul grants spells, favored soul spells are arcane then favored soul grants arcane spells. Imho, if that reading doesn't fling, well, expecting to be able to give arcane spell casting to the favored soul via feats was probably worse.
Of course this relies on a really specific reading of spell versatility and it wouldn't really work. That, and the huge feat investment to meet prerequisites and be viable when not using the trick was what at the end kept me from using the build. I might play it in gestalt, someday though