Thanks for the kind words! You can actually run .NET Core apps already, but the tooling/CI story is still lagging (primarily because the .NET Core SDK is still in preview and needs to be updated to the revised .NET Core project/solution structure).

It's pretty straightforward to publish and deploy binaries from your own machine until the SDK graduates from preview and betas ("RTM" is expected later this year) -- take a look at this discussion for more details: https://support.appharbor.com/discussions/problems/79972-asp...

There are no current plans to offer Linux-based instances, but Windows Server 2016 will be available soon and brings some very exciting and long-awaited features to the table, that will be integrated in AppHarbor products as soon as possible. Stay tuned for more information on that :)