A lot of us lurkers here at MapleRoyals are upstart developers, typically college engineering students from world-class universities. I personally would be interested in how the code for MapleRoyals works, and would be willing to contribute to it. Why not host the code for the Beta server publicly on GitHub and allow developers to contribute? With so many eyes of passionate people looking over it the code would have great chances to improve.
The current source is based off of Odin MS which can already be found easily. The new source is being still being written and has no reason to be Open Source. There already enough hacks and exploits that can be produced when people don't have access to precisely how the server functions. Handing out code will only make that worse.
Hacks and exploits is exactly why the MapleRoyals Beta needs to be open sourced. Open source projects have many more eyes looking over them and allow for bugs to be patched more quickly. Linux, the pinnacle of modern operating systems, is open source. And nearly every Big Tech company is open sourcing their infrastructure, or uses code that is open source. It's myopic to assume that open sourcing a project would motivate new attacks... If somebody has that much time on their hands they probably would have found another way to hack anyways. Moreover, I'm talking about open sourcing the beta only. The beta is still in development, so if there is an issue it will be confined only to the beta server and not the main server. Open sourcing would allow those issues to be identified more quickly and patched more quickly. I am confident that open sourcing will be of benefit to this server.
Chances are they'd sell off the source when Royals goes byebye. Going open source would be throwing away money.
With the amount of effort on the new source, no it won't be open source, there is no need for it. Kevin has done a tremendous work already.