I think it would be amazing to have scripting, like JS integrated with Mythruna. I've already read some where else you might want to make money with Mythruna. One amazing way woudl be create scripts everyone could buy (very cheap, but as people build their worlds, they would buy more and more scripts, and it would give a good profit). These scripts would be executed directly in the server (as the scripts would be made by you or someone of your thrust, it wouldn't be any safety issues regards such feature, and as the server is also made in Java, the same script engine implemented in the client would also be implemented in the server.) However people may also build their scripts, which are executed in the user client. This would allow people to build dynamic stuff, like doors which react to events and would even allow, for example, just a few people to enter in some place.
This would be also an amazing way to create mobs, as long as everyone would create their own "sculpt" and give them life!
I recommend JavaScript because it's a very common scripting language, there are a lot of engines to execute JS (at least there are for .NET, I have already experience in integrating it with VB.NET) and (almost) everyone knows it.