Well, if FF lore has anything to say...
the Double Attack materia in FFVII turns into Quadruple Attack materia.
Though, being able to QA would maximize hits when dual wielding. However I don't see 5% base, unmeritable being too over powered.
TA should get a buff for THF's by 99 anyway, 5% base, +5% merits, they should get a TA II by 99, if not TA III in my opinion, not that my opinion matters much to SE.