I was always under the assumption that the pacts could be a little loose and that a Fiend could actually lead you to have a hexblade "patron" with enough justification?
emphasis on " with enough justification".
We should assume that many players are not familiar with DnD.
It is easy to confince players that your patron is a fiend if you have made a pact with a fiend.
It may be harder (but definitely not impossible) to convince players that you become a hexblade from a pact with a fiend, when they can select fiend as patron.
I hope they add hexblade, but I would not bet on it.
Prof. Dr. Dr. Mad S. Tist 
