Your suggestion sounds fine, but in all frankness, I think many people get numb to this particular request because it happens so frequently. Here’s another request for the same feature that came in literally yesterday: Crossfade anomaly
Each version of the request has a slight variation… for instance, in your explanation, the last part of your original post indicated that moving the second clip would create a gap or need a gap following it. I’m not sure how this works if there are three clips in a row with transitions at each junction and somebody tries to move the second clip. There is no existing gap to move the second clip into, nor do we want a gap created if we move the second clip. You had a good goal of not altering the transition to the right because it may be off the screen and unnoticed, but creating a gap off the screen would be just as disruptive. There would probably be a need for some ripple work to make this function intuitively, but the mechanics of that haven’t been fleshed out well by anyone either.
Even if a good alternative was found, this is an open-source project meaning that demand far exceeds the supply of programmers. New features do get added to the priority Roadmap, but this feature has historically not been at the top of the list in terms of urgency.
So reaction-wise, you are in good company with your desire to change the transition functionality. But this also has to be balanced with people who like the feature just the way it is. Either way, we’re at a bit of a stall until the details are hammered out and the request gets priority on the Roadmap. And this assumes that Dan or Brian will like the idea enough to justify working on it. 
In the meantime, since you’re looking for a way to change transition length without altering clip length, you could use the traditional two-track fade-in/out method. If you have ripple turned on, it’s pretty intuitive the way the following clips shift around.