Hello Peter,
I would like to upgrade to the latest stable Mono version, which is 4.2 at the moment. That is in rawhide already, F23 has Mono 4.0.
Is there a LTS release in the mono 4.x release?
Unfortunately no. There is just an alpha, a beta and a stable channel: http://developer.xamarin.com/releases/current/
What do people think on this list?
What's the future of Mono with an open source MS .Net core?
That is an interesting question. I found this article: http://thenewstack.io/the-opportunity-of-net-core-and-why-it-will-not-fade-a... It says that .Net core will not replace the .Net framework (which Mono tries to implement). Especially for desktop apps (Winforms, WPF) there is no replacement in .Net core. Though winforms is deprecated even in Mono but still works for basic things. WPF has never been implemented in Mono. KeePass uses winforms in Fedora. I wonder if MonoDevelop (GTK#) one day would build with .Net core, but I think that is still far in the future.
By the way, I have a copr repository to build dotnet core for Fedora: https://copr.fedoraproject.org/coprs/tpokorra/dotnet/ to have something similar as it works on https://dotnet.github.io/getting-started/ for Ubuntu 14.04. I have not actually used it, RC1 failed to build on Fedora a month ago when I tried first, but current git master builds now. Now there is still trouble during the installation phase because there is a nuget call. I will look into this another day...
Timotheus