I may have not express very well So I think we don't understand each other: iirc the page User_talk:小躍/Flow didn't exist when I've created the Flow board on it. User_talk:小躍/Flow/存档_1 has been created automatically, but was not relevant.
This needs clear reproducible steps. The description makes it sound like you created https://zh.wikipedia.org/wiki/User_talk:%E5%B0%8F%E8%BA%8D/Flow as a normal page before running EnableFlow.
If the page exists before EnableFlow is run, it needs to go somewhere. We can't just delete it, because it could have old revisions, and we don't want diffs and history of that page to break.
(Checking whether it only has a single empty revision seems like an overkill special case to me, and even then there's no reason to break the oldid for that revision.)
I am the one who suggested this to Trizek. I think what I meant has already achieved. And User:小躍 is a really special case here.
And if anyone are interested in the details: User:小躍 has created the page User_talk:小躍/Flow (with no content) before requesting for Flow activated on User_talk:小躍/Flow, and the EnableFlow tool moved that empty page, but it was meaningless so it is deleted after user request. So I was thinking if a check for meaningless history (e.g. that user created an empty page) or empty history (i.e. non-existing page) would be meaningful. Now I know it won't move anything if the page requested had not existed before activation and I agree that the check would be an overkill.
I guess this could be closed unless Trizek has anything to add.
Thank you again Trizek for the advocation and others for your valuable opinions. I'm sorry if there are any misunderstanding. :)