I honestly have no idea how you could make the Binder work in the design language of modern D&D.
I wanted to say its not just rhe design language but also the gamedesign space of 5e but
@Kurotowa Yeah, I'm not necessarily saying the level of complexity of D&D 5E is bad (though for me, it sits right in the uncomfortable zone of not being complex OR simple enough).
You kind of said the same thing later.
Ironically, I think Binder is a class that could be better expressed in both simpler AND more complicated systems.
I think this has not only to do with the complexity bjt depth of 5e and game design space.
I think Beacon or even strike, which both are more streamlined than 5ey have a broader range of possible abilities than 5e. Just from the way they are designed. (Longer combats (more turns), more importance of forced movement and positioning and different roles and allowing more complexity outside spells).
Also I hope 6E will be more streamlined than 5e but especially I hope it will have again a way bigger design space.
Having said that here how I would make a 5.24 binder:
Level 1 fake pseudo subclass (like druid or priest or kind of druid with fighting style vs canteips) to make it kind of work before level 3 and you can change it every morning. Maybe giving 3 choices here.
Level 2?? Maybe improve the fake level 1 subclass.
Level 3 instead of a subclass you can choose each day 1 vestige. The vestige decides which fake level 1 subclass you choose. It gives you some other passive effects and 2 "once per shortrest" abilities. Each vestige has like 2 parts. The level 3 vestige gives both parts.
Level 5 2nd vestige, but only half its part (like 1 short rest ability).
Level 7 improved 2nd vestige. Gives full vestige abilities.
Level 11 3rd vestige first part.
Level 13 3rd vestige full
Level 17 4th vestige first part
Level 20 4th vestige full.
Each vestige first and second part each has 1 passive non combat ability. 1 passive ability helping in combat, 1 active ability per short rest.
Each first part of a vestige gives an "attack option" (cantrip, good weapon proficiency + Weapon mastery, but maybe also "hunters mark" (proficiency times per day) etc).
Each second part improves this attack ability. (Cantrip improvement (like wis to damage, or additional rider), fighting style, hunters mark needs no concententration etc.)
Level 6, 10, 16 give feats, but they can be changed if 1st, 2nd, 3rd (level 6, 10, 16) vestige is changed.
Not ideal, but uses the 5.24 framework "only" needs to break subclass a bit.