We are currently working on the new Advanced Arduino Project Subsystem that will make it possible (and very easy and intuitive) to manage Arduino projects with Visual Studio. If you would like to get notified about the new releases, please consider following us on Twitter.
Yes, we are expecting to release the next preview with Arduino support in the next 1-2 weeks.
If you buy a license now, you will be able to use any VisualGDB version released within 1 year from your purchase. This will definitely include v5.4 that is currently in preview and might include the next major release, depending on the exact release schedule.