How is EK not... oh, like an arcane half-caster class... what'd the sub-classes be?
I don't recall much about Duskblade beyond 'yeah, that's a gish' and I don't think Swordmage would translate well. Dragon Disciple I don't remember at all.
Swordmage translates very well. There are several DMsGuild products that translate it with varying degrees of caring about repeating what an older edition did.
Monk or Warlock chassis, tight thematic spell list with bigger expanded subclass spell lists than most classes use, core features of mobility, tagging/marking enemies (doesn’t have to be a defender mark), and unique abilities like throwing your weapon 60 feet to make “melee weapon attacks” from range, and a spellbook if I’m building it. It’s a sword mage, after all, not a “Spellblade” or whatever, it’s a warrior and a mage. Spellbook.
Subclasses would be:
a Shadow Hand who animates their own shadow to fight beside them and can animate enemy shadows to debuff enemies, and step into a shadow they’ve animated and out of another.
A lightning themed vanguard type who can do things like turn into a lightning bolt, doing a line of lightning damage, and ending the action at the opposite end of the line from where they started, expanded lightning lure, etc.
A telekenetic warrior that throws their weapon around, explodes it, sends it in wide arcs to attack multiple targets that aren’t close together, etc.
Related to above, a “totally not a Jedi” with invisible mage hand, catapult and other “throw stuff around” spells always prepared, and some limited telepathy.
A Dragoon that has a magical mount and can leap into the air to do big “as an action, blow up that guy in particular” attacks, etc.
Etc