A half-caster with ritual casting and extra attack, is what that translates most naturally into mechanically, with different Esoteric Orders for subclasses at level 3, and at least 3 different Aegis options at level 1 (in the OneDnD model. In the 2014 model you'd flip those), basically mixing the chassis of the Warlock and Monk. Spellcasting at level 2, I guess, to reduce MC cheese. I'd rather have level 1 be spellcasting with ritual casting, mark, and aegis.
You also gain a mark at level 1, and the aegis you choose gives a special benefit to using that mark, with an upgrade aroung level 6-7, and again around level 11.
Aegis format: You gain a special AC calculation. I'd settle for unarmored defense, Int. This is regardless of your Aegis choice. Then, you choose between, let's say:
Aegis of Protection - Your mark causes marked enemies to treat spaces within 10ft of you as difficult terrain, and anytime an enemy within 20 feet of you that is marked by you deals damage to an ally of yours, but not to you, they take damage equal to your intelligence mod. This damage scales up with levels, and you gain a PB/LR teleport and attack reaction at level 7.
Aegis of Pursuit - Your speed increases by 5ft, you can dash as a bonus action, and creatures marked by you have to make a saving throw in order to move away from you? something like that, basically more like the 4e avenger than the 4e swordmage.
Aegis of The Elements - This is a more control focused aegis, that lets you deal elemental damage easily, and you pick an element with a long rest, and your mark gains a secondary effect based on it, and later you get a defensive effect based on the chosen element.
Aegis of The Challenge - maybe an aegis based on forcing enemies individually to focus only on you, with very duelist-focused benefits?
Esoteric Orders:
Order of The Goetic Circle - These swordmages lean more into ritual magic and calling powers to them. That might mean they get a few summon spells, or more spells that fill their body with power like spirity shroud, or it might just mean that they use rituals during rest to put self-buffs in place. Either way they get Magic Circle and Banishing Smite.
Order of The Radiant Dawn - Divine stuff, bursts of radiant damaged, etc
Order of The White Lotus - Focus on swordfighting, bonus spells are all weapon smites and personal buffs, and compelled duel.
Order of The Temple Guardian - draw inspiration from warrior-monks
etc