Open Source Readlang
Now that you are working for Duolingo (congrats by the way!) and have declared Readlang has been declared "feature complete", have you considered open sourcing Readlang? I understand that you don't have the time to devote to new features, but I'm sure there are developers out there in your user base (like me) who would be more than happy to contribute to the project (even if you get the money for operating the service). There's so many good feature requests on here that I'd love to see implemented, and I think open sourcing and embracing community contributions would be a great way to see them made a reality.
I am sorry to hear that Readlang has been declared "feature complete." It's not, as evidenced by all the great suggestions here. If Readlang is no longer supported, then why keep these forums open? Is it only to keep the appearance of a viable program so they get new subscriptions? Readlang is a good program, but without further development it will quickly be deprecated, as all software does that loses development. +1 on the suggestion for the developer to consider contributing the project to open source for future enhancements. Maybe a problem with any current revenue stream, but at least the program stands a chance to survive if development continues.