Do we stop supporting external software?
No do not stop, with commentary.
The problem with old versions is that they clutter and confuse searches and explanations for current users of current software.
I'm of the opinion that asking questions for old things should be allowed, but only if they are specifically identified as such. I think truly solving the above problem is done at the underlying website/engine level in the same way that someone could search for help, but prioritize newer responses. I have personally found great value in finding old solutions to awkward partly-related old questions for my current-software-problems. The fact that those questions have been posed recently or not is irrelevant to my value of them.
"supporting external software" creates the problem of distracting the attention of answerers. They ought to pay more attention to current software for the larger audience and for the explicit purpose of this site.
Explicitly support: If more reasonably implemented (better identification/search), even though the above answerer-distraction problem remains.
Explicitly do not support: If it clutters and could obviously threaten the purpose of this site.
Since no change at the engine level is proposed/forthcoming, I think some form of do nothing makes sense.
Do nothing, discourage feels right to me. That is, allow it to become a cultural norm for people to ignore these problems or not spend very much time helping, and to let the questioner know why. Bounties then remain a possibility to those questioners.