The best advice I can give when it comes to multitasking Swordmage is "don't". However, I guess they'd be like the warlock, but you'd also gain proficiency in one handed martial swords and medium armor. Dipping far enough to get Elemental Blade from elemental Dervish would be great for a twf fighter. Dipping for ever-present escort is great for a sword and board pally or fighter.

I need to rework Student of Malediction.

I'm adding a fourth subclass that focuses on further casting.