We have several things on our roadmap, the sequencing of them will depend on customer requests and whether or not we run into unexpected issues.

• Xamarin Support:  We have been steadily working on shipping support for using VistaDB with iOS and Android devices.  We do have customers doing this in a preview mode but are waiting on improvements from Microsoft before we can make this easy enough to do to meet our goals (currently you have to compile VistaDB from source for the target platform to get it to work reliably on iOS and Android which we don't consider reasonable)
• New Data Builder:  We shelved for 5.0 a completely rebuilt Data Builder application that you can ship with your application for use in the field, supporting a friendlier UI and asynchronous operation.  This has been revived and we're working on it for a future update to 5 or for VistaDB 6.
• Entity Framework Core:  (Formerly Entity Framework 7).  This uses a completely new provider model and is relatively immature compared to EF 6.  We hope to ship a new EF Core provider (that will still require the full .NET framework, not .NET Core) as an update for version 5.
• Big Performance Improvement:  During development of version 5 we identified a fundamental design choice made back when VistaDB was first written that significantly reduces scalability when performing multiple queries in the same process at the same time.  We have a strategy to redo the low-level VistaDB implementation to address this and possibly gain a significant amount of performance, particularly in operations that are slow today.

That is probably one of the toughest areas for us to make real improvements without writing a completely different VistaDB that's an actual server.  The core problem we face is providing a reliable, consistent database through SMB File sharing.  Put simply, networks are just too slow at that tier of an application.  We've looked a few times at a server version of VistaDB but were cautioned each time we did an analysis that there likely isn't sufficient market to justify the engineering and maintenance costs of such a product.  But, we're willing to be proved wrong on that point!

Following up on this - work is proceeding with Xamarin support.  We're going down the route of producing a different assembly for each platform which appears to be the best approach.  We currently have an iOS assembly that is passing all but a few unit tests, one of which may ultimately reflect a limitation of running on Unix.

If you're keen on trying out iOS please reach out to support and we can send you a binary to try.  Meanwhile, we're going to turn our attention to Android.

We're expecting to have that as well.  Any customer that's keen on giving it a try should contact Support for a preview version.