I saw your request on the mailing list and just thought I would give you my opinion.I'm no Color Management expert but I have been working in prepress for 17 years now and have had some experience with CM.

I have been using ECI RGB as the standard RGB working space at my company for few years now and it has been working wery well for us.If you are able to compare this space with other working spaces (such as Adobe RGB for ex) in a 3 D graph you will see that it is better for prepress work.Although it is similar in size to Adobe RGB it contains more printable colors, or should I say it fits better to a normal gamut of a printing press.It is mainly in the yellow/green region of the color space where this is obvious.I have allso been told by Color Management experts and consultants that becaus ECI RGB is based on D50 instead of D65 it works better as a editing space for prepress work.This does'nt mean that ECI is the ONLY working space for prepress, you can get as good results using some other space that is large enough to contain all printable colors, but in my opinion it is a very good working space and I' m going to keep on using it.