A sink can seem restrictive or it can feel like a thing you'd do anyway. A good sink is repairing, because it makes sense and it's something you'd do to keep playing, and it doesn't feel like a restriction, more a necessity. Binding equipment on the other hand, is artificial and actually feel like a restriction. mechanics is basically how to play with the illusion of choice, physics, movement, economy. It's not really there it's just designed to seem like it is there, and the way to successfully implement a system that restricts the player is to alongside with it make it seem like an investment on the player side rather than a straight up restriction, like repairs, or less frequent drops. For example, a good way to make people sink money into the system is to make an area that when finished, rewards the player with a piece of equipment, but the journey there is costly, it would require the player to buy potions, repairs, buy extra soul gems and so on. Not that it hasn't been done before, but you get the point.
I also don't believe that I, you or anyone else should come up with a solution, but I think it's it's important to raise the question so that the actual developers get something to think about, and that is far more important than the community cooking some semi-good solution to a complex problem. That said it's important to challenge systems that we love and at the same time acknowledge how desperate of a design desicion they are in core, I don't see the point in defending it (not saying you do, but I've had my share of those who do) considering it's biggest flaw: blatant restriction with no ties to the gameworld or gameplay.
But now I'm getting ahead of myself, I get your point and it's valid, but I'd personally rather see something different. It's sometimes a good idea to invest some brain-points to come up with an idea that blend seemlessly into the gameplay that can replace the current more noticable system with something new, and it doesn't even have to be similar, because all of those systems have the same goal: to sink money/gear or other acquirables, and the sooner we can replace the bind-mechanics with something better, I'd be a much happier person.