The TCDIALOG is not always function complete. If its output could be copied to the clipboard or pushed to the top of the command stack (like Ctrl-K), then it could be recalled and supplemented before execution.
Since the user can only discover that TCDIALOG doesn't cover all options while in the dialog, my original suggestion of an option /N has the wrong form.
There are two ways to get into the TCDIALOG, e.g: with /= or with TCDIALOG. Both variants are added to the history which is useless since the're not finished commands. If you would reexecute them you'd have to go through the completion process again. The latter can be suppressed with HISTORYEXCLUDE but I suspect the former is is the one more often used. It would be more useful to replace them with the "finished product". But, even then, the TCDIALOG is not always complete which means you have to edit the command before execution. For that purpose, it would be helpful if there was an extra button with which you could close the dialog and make the partial result available on the commandline (via history or clipboard?) *without* executing it.
The edit control you mentioned does not contain the command, only the options, so it is incomplete in yet another way.