.NET improving faster than the JVM would be a very hard thing to measure or even estimate. There are very exciting and impressive things happening in JVM land, for example Graal and Truffle.
I think it's pretty disingenuous to say those things are hard to measure or even estimate. Java and C# are close enough that you actually CAN measure them in a pretty useful way.
Java has been behind the curve for YEARS as compared to .Net with perhaps the exception of the cross platform aspects and the more permissive licensing.
The closest thing I can think of is PyPy, which like Graal+Truffle lets you write a dynamic language in a high-level way, but still get specialized JIT compilation "for free". (In PyPy you write an interpreter, in Graal+Truffle it's more declarative.)
Both PyPy and Graal+Truffle achieve state of the art performance. I'm not aware of any dynamic language on .NET coming even close to that.
Both IronPython and IronRuby have used this for years.
The "Day 1" comment was specifically pointed at the read-between the lines for Graal, which is basically to create a real IL for Java instead of using the InvokeDynamic semantic that is currently envogue for Scala, Clojure, etc. .NET has had the multi-language one VM paradigm since day one.
The fundamental issue is that dynamic languages need JITs that are very aware of their internals. It's not enough to just emit some code interspersed with PICs and to add fast dynamic dispatch. You also need to speculatively compile and deoptimize in a way that is specific to each dynamic language. Without that, IronPython and other dynamic languages on .NET are often not a little slower but 10x slower than the same languages on the JVM or PyPy.
Graal together with SubstractVM offer AOT compilation and is also being used by AMD for the GPGPU support targeted for Java 9, latest Java 10.
Truffle is more of a AST manipulation framework for nodes that can be fed into Graal for compilation.
Then there are those meta-circular JVMs like JikesRVM which are done in Java.
Sumatra is planned for integration latest by Java 10.
There were a few Java ONE 2014 and JVM Language Summit Presentations.
JRuby: The Hard Parts, Reduction on GPUs, GPU/JVM Cooperation
http://www.oracle.com/technetwork/java/javase/community/jlss...
Ruby on Top of Graal
https://old.parleys.com/share_channel.html#play/543f88bee4b0...
Sumatra OpenJDK Project Update: Parallelize Yourself with the Stream API
https://old.parleys.com/share_channel.html#play/543fa782e4b0...