In Virtuoso there is status indication telling about selections - how many items are selected, how many nets, instances or objects...
Something similar might be useful in KLayout?
Maybe the properties form could also indicate e.g. selection # of ##?
One old piece of s/w even reports the edge length and area of selected objects, but obviously that may be more involved and could affect performance...
In the meantime, is there a simple way to count the selected items in the Ruby console?