Mobile web projects/GettingStarted

I want to be able to deliver tasks to users based on certain categories/criteria (e.g., all stub articles that require copyediting)

Can we use it to deliver random tasks on mobile?
Yes, as long as those tasks involve editing articles (see further info below). If none of the tasks we want to use on mobile involve editing articles, we probably don't want to reuse GettingStarted.

Do we have to do any additional work to reuse it?
The special page (Special:GettingStarted) would require only a small amount of modification (switching the task sets based on it being mobile and some style tweaks). The in-article interface would require some restyling. The GuidedTour aspects would need to be changed for mobile since these assume a desktop interface. In particular, it directs attention to the maintenance tags (which we hide on mobile), and the section editing links (which we don't yet have, but probably will soon).

How hard/possible would it be to make it global instead of enwiki-only?
Right now the tasks served by GettingStarted are defined based on en.wiki specific categories. The definitions themselves are specified in a global config var, $wgGettingStartedTasks. The tasks can be overridden per wiki in the cluster config files, but this has to be done by us (not by the wikis themselves), and we would have to find out what categories are appropriate for each task type on each wiki. This is not a very realistic or scalable solution. If we wanted to deploy it outside of English Wikipedia, we would probably need to develop an on-wiki configuration system so that individual wikis could handle their own configuration.

How hard is it to add new tasks?
It is relatively easy to add new tasks as long as they are based on article maintenance categories. You just have to specify the category, some i18n messages, and an icon for the button. Currently, however, there is no mechanism for adding tasks that are not based on article maintenance categories. If we wanted to add such tasks, we would need to handle the task generation for those ourselves and modify the special page to surface them (or create a separate special page).

Additional considerations
E3 is considering revamping GettingStarted to have a completely different workflow. In the new workflow new users would not be redirected to a special page, but instead there would be an overlay added on top of whatever article they first looked at. The overlay would ask them if they wanted to learn more about editing articles and then they would eventually be routed into a copyediting task. I'm not sure if this workflow would be very useful to mobile or not. E2 says they will keep us apprised of their plans.