You can connect to REPLs over ssh using `ipython console`. Even without EIN, you can use this command (plus several options for ssh connection) for python-mode's interactive shell. With EIN I think it's a little bit easier (if you are using python.el), as it helps you to setup these options.
re IronPython/IPython: it's on the list of things i'd like to fund the IPython team to do, though there have been bigger fish to fry during the past year... most recently getting IPython on to Windows Azure & Visual Studio. It shouldn't be too hard given the recent rearchitecture. <disc: me @ msft>
Speaking of Windows, anyone out there have recent status on any efforts to port IPython to IronPython? IIRC removing CPython implementation dependencies was explicitly mentioned in the general design goals for the 0.1x refactoring, but I couldn't find anything beyond this when I looked into it a few months ago. I ask because it's actually a project I've seriously considered picking up myself if it's not nearing completion elsewhere.