My take on it is that once Kaladin swore the Third Ideal then those bound to Kaladin by loyalty and honour gained the ability to hold Stormlight and nothing else. But even that is a considerable ability, as the Lopen's arm growing back proves. Remember as well that Stormlight doesn't give you new abilities but perfects your existing skills. So to take one example, Rock should now be an absolutely incredible archer if he ever decides to use that skill again.
So I don't think Lopen or any of the other bridgemen are proto-KR, but they are Squires. And of course a Squire is a Knight in waiting. So if Honourspren ever do return in numbers, they might just be attracted to the people who follow Kaladin. An Honourspren binds things and is attracted to those who bind, after all.
Right now I'd say the Squires are limited to the original members of Bridge Four, but given the way that Kaladin is training the other bridgemen - modelled on how he trained Bridge Four - I wouldn't be surprised to see the entire force becoming Squires in time, and the officers leading them becoming Windrunners themselves.
What's interesting to me is if Shen Rlain can become a Squire. Listeners aren't supposed to be able to form a Nahel Bond with a Spren but the nature of the Knight-Squire bond might be different enough to work. And I like your idea of Squires being able to feed Stormlight to their Knight Radiant.