It's a generic thing in the engine and it's basically done automatically. If a research applies to every entity in a given category, it just writes "All" rather than listing out every single one. Of course in the case of starbases there is only one, but it still does it.

So no, it's not really a hint that more are on the way.

played advent lately?

I am well aware that they have a culture feature. Same as all 3 races can do trade/econ things too... I was just pointing out the similarities of adding additional starbase types....