Adding at least 'dumb indentation' (repeat last indent) to the REPL would make it at least a bit more usable.  (This still would not be a good as an IDE, like IDLE, that does smarter indentation, such as adding an additional indent after a compound statement header ends with ':'.)

The simplest patch would be to slice and echo the initial whitespace (spaces and tabs) of each line that needs to be followed with a secondary prompt.  What I don't know is whether, on every console, a printed tab always has the same effect as a tab entered by a user.
Testing would be needed.