I'm really uncomfortable about making the repl and file readers differ, especially to the point of being incompatible.
About a custom console, I am not sure there is any reliable way to detect when a user has pasted code into the console. (That sort of thing is probably very OS dependent.)
Even if you did set up a timer like you propose, what would it do if the user recalled some lines from a multiline entry in history? I think most consoles would only pull up one line of history at a time, so the user would have to go through each line and enter it individually. And the timing would be such as to be indistinguishable from direct input from the user.
As for infix math, if you created an infix marker like
