By the way, thanks for taking the time to try it out and think of all
possible issues.l

> I have two archives configured: GELPA and MELPA. After Emacs was
launched, I can `M-x list-packages', and the list starts with 2048-game, @
and abc-mode. 4clojure (and many other packages) is listed as "incompat".
>
> But after loading ends, 4clojure gets inserted at the second place. If I
quit it and call `M-x list-packages' in the same session, 4clojure is there.

I don't get that bevahiour from emacs -Q, but there was a problem with the
incompatible table a few days ago. Maybe your elc file is outdated?

>> The suggestion was not to use a question prompt, but to simply message

>> "Package refresh done, type g to revert buffer" instead of the ususal
>> "Package refresh done".
>
> If it's a message, it'll disappear after the next command. Then, I can be
only sure the list is refreshed if I don't select any items.
>
> And this information won't be present in the interface, aside from the
transient message. Kinda suboptimal.

Just like any other keybind. That's more of a general issue with the
package menu or Emacs itself. We can add "g-redisplay" to the quick-help
menu under `h' (which, btw, could use some improving.

>> No. If she reverts, any "i" marks will be forgotten. This is a flaw of
>> this approach, but one fortunate consequence is that there won't be
>> any such inconsistency problems.
>
>
> No, I mean if she agrees to revert after the installation has started (or
maybe just the downloading part started, and hasn't finished yet).

Ah, I see. Then we're fine. All information needed for a transaction is
gathered the moment you hit `x' (before you even answer `y'). Whatever
happens to the buffer after that is irrelevant.

>> The only
>> difference is that now the user has a brief chance to see the old
>> package before it is brutally taken beyond her reach.
>
>
> One could say it's worse than never seeing it, though. Wasted effort.

Yes, but you're wasting a few seconds of effort on a situation that will
happen very rarely. If that were a frequent occasion it might even be
infuriating, but how often do compatible packages become incompatible?