I wonder if they backport dtrace so it can be used on older Windows Servers (2012 for instance)? Or maybe they can somehow make it work in .NET Core only for such operating systems - it could still be very useful.
Not too likely. The hard part of implementing dtrace isn't porting over the program itself, it is the huge number of OS kernel hooks required to instrument. Those are unlikely to be back-ported. The really interesting question is now that they have the hooks, will they consider making additional interfaces with their own languages (powershell anyone?)
Unlikely. Dtrace needs support from many OS components, including kernel.