**Feature summary** (what you would like to be able to do and where):
Rather than having to pick individual wikis it'd be useful to be able to pick specific subgroups that're managed by the platform.
E.g.
* All wikipedias
* All wikitionaries
* Top 10 wikis by traffic (might require splitting enwiki out given its different rules for the traffic-split on edge-unique)
* RTL language wikis
I'd imagine this might want to work by prefilling the widget, so that specific wikis could then be un-selected.
**Use case(s)** (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
There are presumably common targets for experiments, and I'd like to be able to quickly set those up without having to manually look up a list and copy it in.
**Benefits** (why should this be implemented?):
* Easier to create experiments.
* Less likely to make targeting mistakes while configuring the experiment.
* Centralizes work so that individual experiment creators don't have to individually recreate "okay, what's the 50 most popular wikis?" each time.