It certainly is worthwhile pursing this in some fashion, since at the very least the existing error message needs to be improved.  But perhaps there is something more that can be done to gracefully handle this case, instead.  I think the next interesting question is to find out why an invalid home directory causes idle to not start up.  There's no obvious reason why that should be the case in principle, so I suspect there's some error handling missing somewhere.

This probably also applies to 2.7; someone should test that.