Just to justify why I keep playing Devil's advocate to new suggestions
I still feel that there is an awful lot in Z39.50 which just doesn't get
used. I know Rob would argue that is what makes Z39.50 powerful (and I
know Rob is one of the few who actually uses that stuff), but in general
we have a lot of baggage in Z39.50 which is there due to it being a
clever idea rather than because people implemented it (a few cases
someone said they needed it but never actually implemented it).
My personal opinion is we should keep SRW/SRU fairly simple and not
introduce anything because we can but because it is really needed (real
world case and usage scenarios rather than hypothetical).
At least in version 1.0 - it seems to be that the successful protocols
are ones which were extremely simple in the first release (HTTP, HTML
etc.) in many ways naively so. But they only started to add the
complexity after they'd hit mainstream acceptance. If you hit the world
with an all singing all dancing protocol from day one, its complexity
puts people off.
As I've said before, cynical though it may be, I see ZiNG as a marketing
exercise as much as anything else!