DND_Reborn
The High Aldwin
My thought is that with access to more feats and all the subclasses (we have 92+ now) there would be enough to get the flavor of multiclassing. Please note, I am talking about 5e as it is now and making the minor changes suggested.
I figured that was your thought process, but IMO most of the archetypes really aren't that good. I can't tell you how many times a player is making a character, looking over the archetypes when the times comes, and not thrilled about any of the choices. More often than not it becomes a which is the least bad choice.
Simple "multiclass-like" subclasses would be fine. Things like Arcane Trickster, but without the limit on what types of spells they choose (same with Eldritch Knight).