You have made a good point. But, let me give you a scenario:
- A user posts a topic.
- SS and GT are currently online.
- SS opens the topic. He opens the “Reply” dialog box and starts writing.
- Say 15 seconds later, GT opens the topic and its Reply dialog box.
- Now, GT - who hasn’t started writing - sees “SS is typing…”. GT thinks: “All right. Someone’s already writing it out. Let me sort out another post.” SS also sees: “GT is typing…” on his side but he has already written some 4-5 sentences and now would not stop writing since SS will not give up his hard written post (even if it’s just 4-5 sentences). Also, GT will immediately quit the Reply dialog box within 5 seconds and so the notice, for SS - that “GT is typing…” will quickly disappear.
At least, this is the way I think how it would work. Even if SS and GT both stopped writing, then the topic would still be there in the “Latest” tab and one of them might pay his attention back to it within few minutes.
Alternatively, we could also attach to this feature something like:
N users writing since %time%; click to see who
where %time% is the time passed since the earliest user (out of the N) began writing. This way GT would be firmly sure that: “SS has been writing since 1 minute; must have written some large amount…”
Or, yes, @jomaxro made a good point, some warning modal like:
SS has been typing since n minutes. Are you sure you wish to continue?
And I agree with @jomaxro regarding the fact that -
“same time posts” that made an in-progress reply redundant and moot.
would be a big “turn off” for user engagement (though I too am not even a novice in user engagement; but answering from my common sense)