Something I've wanted to see for a while now, but as someone said in an earlier post not all of the advanced classes work. Thf > Nin
I think it's a neet idea, it's a bit of the classic Final Fantasy mixed with Ragnarok Online. If you're going to mix match jobs to form branches it also has a bit of Secret of Mana thrown in. Personally I'd rather just see a following of the original FF and have flat out advanced jobs. That way alot of the old armor, job abilities, weaponskills, spells, etc... could be used. Perhaps reduced timmers on abilities and higher base stats with some new items added in. As well as few advanced class only armor sets.
I won't hold my breath for any changes this major though.