Yes, that's true, you can get a list of unconnected profiles, but it's not quite what I was looking for.
The advantage that I see in Aleš's geographic reports is that you can see all the branches with at least one profile for a person who was born, married, or died in a specific country (or, in some cases, subdivisions of a country), sorted by the number of profiles in each branch.
Many Connectors prefer to work with the largest available branches, so they can connect more profiles with the same effort. So I believe that Aleš's report have been very useful because they allow connectors to target the largest branches with a connection to the location they're working on.
So my thinking is, how can we give that same advantage to Connectors who prefer to work on a particular surname, rather than a particular location? That's why I suggested having reports that don't only list the size of the branch, but the number of profiles with the designated Last Name At Birth in that branch. Because you could have a huge branch with only one profile with the surname you're working on, and another branch which is smaller in absolute size, but has a lot more profiles with that Last Name At Birth.
Another drawback of the standard WikiTree unconnected report is that it tops out at 99 connections, and just shows "99+" for branches larger than that. Since the 100 largest unconnected branches all have more than 200 profiles in them, the standard report isn't a good way to identify the largest branches.