This can be disabled via a:options.isAllowDigraphs = 0. The query functions for register, mark, substitute confirm, history recall, and confirmed filter disallow that as it's not needed.
Make "q" return the confirmed results so far, so that "y, q" works like "l" (similar to :s///c). Only <Esc> now actually aborts and returns the original, unfiltered List of items. Returning an empty List doesn't make sense here at all, as the user can quit without changes from the rendering dialog.
To be consistent with the built-in commands like :substitute. It's unlikely that a user uses the same delimiter (e.g. /foo\/bar/) when the delimiter can be freely chosen, and for many delimiters, the backslash in front of it is not critical (but it is for e.g. +.), but better be correct.
Ingo Karkat