As far as I know, neither [Models] nor [Protocol] limits the lenght of
attribute names. Any limitiation in a specific implementation is imposed
by that implementation, not by the spec, so I'm not sure we can do
anything about it here.
Obviously no server allows an unlimited length, as they are all
limiited if by nothing more than available memory. I'm not sure if this
fits into an implementation report. It seems more appropriate for a
certification/branding program. Other than that, it seems like a valid
defect to raise with those implementors who restrict to unreasonable
limits.