If this ever saw print, which do you think would get banned in Modern: itself (along with pretty much every Smuggle card at 3 cost or less) or Eldrazi Conscription?

This seems easy enough to fix, though. It just needs to read something like "Smuggle 2" where 2 is the converted mana cost of the enchantment. By the way, casting cost of the enchantment equal to casting cost of the creature may be a good way to scale this. I have a feeling that this creature with, say, Elephant Guide, would be too good a creature. 4/4 Hexproof that if it dies gives you an elephant for and discard a card? You don't need the Conscription to get abusrd. This guy on round 2 pre-enchanted with Sleeper's Robe should be solid enough.

I really like jmg's suggestion of having a max CMC for the aura. This ability seems really powerful, especially in an enchantment set (with totem armor to boot!)

This is just the same as Academy Researchers. Which are also stupidly good with Eldrazi Conscription, in just the same way Stoneforge Mystic was with Argentum Armor. But the hexproof does take this somewhat over the top.

Fixed.

I think what jmg meant (and what I agreed with) was having a variable smuggle number. Something small like this can have smuggle 2, but a big Aura-themed legend could get away with smuggle 8 (it can steal an Eldrazi!)

Yes, but I think it should only be a small aura so it's like it's pickpocketing someone.

That's reasonable. I like it.