Could digital "real estate" or "territory" be taxed in the same way -- not literal digital territory, like in games, but considering "ad spaces" as virtual territory? I suppose more generally, any "technology company" which primarily makes its profits by virtue of establishing a network effect, wherein they earn ever more money as more people show up.
One possible objection: there are fixed costs for sustaining the virtual territory. It doesn't just exist; at a bare minimum, sustaining the software requires servers which in turn require maintenance, and the software itself would require some developers to fix bugs. But these particular costs can be indicated and accounted for without too much difficulty.
Another possible objection: there are no competitors providing the virtual territory; there is only the one company. If they hadn't created it, it wouldn't exist. So... if this kind of tax was to be executed on virtual territory, the company would have to be broken up and divided into competitors that could attempt improving on things in different ways, and the infrastructure providing the virtual territory would have to be nationalized.
As an example, maybe the competitors can buy keywords from nationalized Google, and then they can change the ad space that people who search for those keywords see; they become the rentiers of that ad space. But to be able to afford the taxes on keywords that are in high demand, they have to improve upon those ad spaces. Maybe they provide a shiny gold effect and sparkles around the ad -- only if the people paying them to show ads for those keywords want it, of course.