Current paper design for Soul Eater has some "marker" debuffs that trigger additional damage or debuffs when you hit those enemies, whether with Eldritch Blast, melee, or ranged attacks. There's some details to still work out, of course.
My suspicion would be that it's hard to really "get it" without playing it, in some ways.
This is a line we considered. We debated having ranged feats affect Eldritch Blast attack speed, etc.What if this one used things that normally improved melee to improve the spell casting? EB already activates based on your weapon attack. What if the devs really dug into this part? Instead of taking SF: evo, GSF: evo, ESF: evo, max, emp, quicken like every other caster, players picked a weapon style and build their caster that way? Basically a backwards Eldritch Knight. Instead of their skills in magic making their melee (ranged) combat better, their skills in melee (ranged) make their magic better.
Regarding multiclassing: We are taking it strongly into consideration, and the enhancements will help there. Just looking at the feat list may give a lopsided view, especially if you just focus on Eldritch Blast damage. We certainly expect some players to build 15/5 builds, with the Warlock levels on either side of that equation. Many enhancements directly or indirectly increase Eldritch Blast damage, so you only need a few levels to gain those boosts (unlike the feats). Someone with only 5 levels of Warlock probably won't be using an activated Eldritch Blast all the time, but an Aura version combined with debuffs from Soul Eater or bonus damage from Tainted Scholar (though Tainted Scholar is the most directly Eldritch Blast oriented tree).
Enhancements allow Eldritch Blasts to cause other things to happen, whether that's adding additional effects when you hit something with Eldritch Blast or giving you new options for passive (auto-attack) or activated Eldritch Blast attacks.
Additionally, effects that trigger on spellcasting work with Eldritch Blast, such as Lantern Ring or Rainbow.