We don't have a good time estimate yet for when Alpha 19 will be ready. We hope to have it out in the next month or two, and we hope to include the new Roche limit fragmentation.
We've been working on a lot of big projects, many of which have a lot of interlocking parts with their own bugs and complexities. It takes a while to get all these parts to play well together, and then longer to get these projects working with everything else that's already in Universe Sandbox ². Universe simulators have a lot of moving parts.
What are these big projects? Virtual reality, improved planetary details, rewritten stellar evolution, and rewritten user interface. And soon we'll have the new Roche limit and total body fragmentation. You can read more about all of these in our 2016 roadmap post:
http://universesandbox.com/blog/2016/01/2016-roadmap/We also try to have a new post up there every week or two. It's not always specifically what we're working on that week, but it discusses some of the things we're thinking about or working on long-term.
Hope that answers some questions!