Sorry, you're right ... it also encompasses the extension model used by user groups in the 3.x platform.
I was thinking of its use in the static datamodel, not for the dynamic extension. But one could provide a generalized facility based on "alter table" (which is what 3.x user group types do).
The "alter table" approach doesn't work for multi-valued attributes, of course, unless you added enough weirdly-named columns to support the maximum number of values or abandoned standard SQL features entirely (i.e. use PG arrays).
So I guess a more accurate statement would be that we could get rid of the attribute values table if we did not support multi-valued attributes. Perhaps it wouldn't be worth it ... as I said I haven't looked into this in great detail yet.
