currently, the following command will fail on pkgconf 2.0:

$ pkg-config --modversion dbus-1 'dbus-1 >= 1.6'
pkgconf: --modversion requested with multiple packages, output would be ambiguous

while it might be a bit redundant to do so in this case, the output would not be ambiguous, and unfortunately there's prior art

furthermore, with the check in place, there doesn't seem to be a way to query a package with both an upper and lower version bound; it didn't really work on pkgconf 1.x either, but it seems to work with pkg-config, so maybe it's worth looking into as well:

root@86a8a87bcfe7:/# pkg-config --modversion 'dbus-1 >= 1.6'
1.12.16
root@86a8a87bcfe7:/# pkg-config --modversion 'dbus-1 >= 1.6' 'dbus-1 < 1.10'
Requested 'dbus-1 < 1.10' but version of dbus is 1.12.16
root@86a8a87bcfe7:/# pkg-config --modversion 'dbus-1 >= 1.6' 'dbus-1 < 1.15'
1.12.16
1.12.16