Technically, there's nothing against an EK binding a ranged weapon. It's completely possible in TT and RAW. There would be no balance issues from such a thing.
The main problems are as such:
1) Currently the "Bound" bonus on the 2 available weapons are shared between EK and Bladelock. While it's fine and dandy for an EK to bind a ranged weapon, for Bladelock it's a little bit murkier - RAW it's possible for them to bind a magical ranged weapon. But RAI suggests otherwise given that you can only summon a melee weapon as a pact weapon (With Xanathar's Guide to Everything providing Bladelock with the ability to summon ranged Pact weapons suggesting that binding them is also intended to be part of Improved Pact Weapon).
Thus it would be sort of odd to randomly have a ranged weapon that reneges on including Bladelock.
2) Mechanically, it seems to be that binding defaults to the main hand melee weapon. It would likely take some work to modify the mechanic to be able to affect a different weapon slot.
3) Even if they did make a ranged weapon with a "Bound" bonus... Would it even compete with existing ranged weapon options? I mean, Harold already provides a Baned effect (Like the Bouned bonus of "The Baneful" provides) while you have powerful options such as Titanstring Bow, Giantbreaker, The Dead Shot, Blightbringer and of course Gontr Mael. Much like how The Baneful and Charge-Bound Warhammer fall off compared to stand alone good melee weapons.
So yeah, while I'm not against more magical items (I feel the game really lacks in some types of magical items) I'm not so sure that a bound ranged weapon will happen. Perhaps modders might provide such a thing in the future though.
