I think seeing some XGtE invocations isn't THAT unlikely, same with feats from there as well. I think the odds of anything outside PHB being added are directly tied to how many new assets and interactions adding them would entail. So eldritch smite would probably not require much in the way of either. And we've seen them make some pretty big alterations to the Ranger, as you've pointed out. Since Wyll is clearly meant to be a blade pact warlock, I suspect that the reason they didn't include pact of the blade from the beginning is that they're conscious of the limitations you're pointing out and are trying to figure out how to fix that behind the scenes, much like they altered Rangers. They just had Rangers ready to go first for EA since they're something of an archetypal class, so starting EA without one would have felt 'wrong'.
