All of the statements here are completly valid and I would like to encourage you working on it further.
You opened your code now to the public and those are the responses you get and you should work with.
Everyone of those guys here and the developers of other libraries have developed projects in their free time and learned from it and maybe built onto this.
The question "what makes your library special" is a very good question you should ask yourself, because it is the target you want your project to be heading at.
However you answered already why your engine is better then Kryonet, it doesn't need to be better then every other engine.
I think the use of Java is a very important approach as Servers very often use Java technology including but not limited to the possibility that the VM can crash safely without damaging the server itself and it is a by far easier language to work with then with C++, also it is THE language for Android.
C# is just Java again but one year in the past, so yeah thats about it.
While you can bind C++ code easily with JNI (and there are also many IDE plugins doing that automatically for you) there are still many problems i.e. using casting and stuff which do not translate great between C++ and Java.
So the "language" you are using is indeed interesting for Java-Developers.
I am right now using Java because of development on Android and C++ turned out in the past to be a huge pain in the... on this platform as there are like a bazillion different smartphone models on the market which is basically the downside of C++ making it even more complicated.
Though for encryption and decryption you might want to implement another existing (C++) library as both parts can be critical spots needing skilled developers to work on.
So I am considering working with your library. Http and Https is part of the standard Java library, I never use TCP in games especially not when multiple Threads are involved (on typical Android hardware!? Very bad idea!) and I don't think the players would benefit from any encryption in my game anyway.
That said I am here for the UDP part of your library.
Do you think games can benefit from your UDP part?
What are the benefits instead of doing it by myself? (My project right now contains no single line of networking code, just an empty thread looping, doing nothing, waiting for something to do)
And how can I implement your library into my existing project?
Then the final and most important question is: Am I allowed to use your code?
I can't find a "licence" or "conditions of use", maybe I am overseeing something but... can't find anything.