Available time, mostly. It’s more complicated than it looks on the
page. Are the counts of individual variables or totals?
Totals.
If the former, is it okay to forego totals by design (seems safe, but you
never know). If the count is of individual variables, are the counts
expected to work in the normal way with match=“any|none|all”?
Yes.
If so, what happens if there is an item with one author and two editors in
the example above (any|none|all doesn’t permit control over sequence
and priority of evaluation – you would get that out of the box with
form=“count” just by relying on substitution and counting the names
that would be printed).
count == 3
A problem you would have with support is that errors in the CSL code
that are not obvious to a designer coming to the new syntax for the
first time might produce results that are hard to connect to the
error. You may get lots of support queries. Are you comfortable with
that?
I’m not comfortable with this use case at all, but I’d like to solve it 
It’s late here, but if my sleepy reasoning doesn’t deceive me,
addressing the use case and retaining the simple syntax in the example
above, you would need to return the count of the first non-nil
variable, and invalidate match=“none|any|all” for conditional elements
that contain a count-min/max (or allow them, but offer first-non-nil
sequential checking as the default, which would be more flexible, but
would also be confusing).
Correct.
Subject to all of that, it would work. You’d need to provide a spec
explaining how all of the possible option combinations should be
handled. It would be nice to have it expressed as a set of tests.
I’m curious so I might as well ask, what is your objection to form=“count”?
I don’t have any particular objection to it; was just trying to
clarify the issues.
Your point is that the counting folds in the substitution logic, such
that we’d avoid the potential problems you note above (that it’s a
little awkward to have to essentially duplicate substitution logic
across different macros)?
That’s a reasonable point.
Andrea, any thoughts on this?
Bruce