Oh man, the dark side of free software is always going to worry me.
Spoiler, click to toggle visibilty
you understand what you want to understand from your limited knowledge and points of view on how this works, You want to use something proprietary but without owning it.
There is no Suehiro IGP or K4thos IGP or Gaciel IGP or Unsou IGP, all those and any more to come are the same, only everyone is working implementing different kind of things and later combining or fusing all in one regardless the repository. (original is from suehiro)
The syntax of how things behave in the game, all the strings, state names, files extensions for you understanding is the basis of the engine, it does not matter if it exist a small file called common.cns or common.zss or common.free, while the base is still moving and executing files that were created for the original mugen there is no way for you to say that there is a free version without it sounding like it is a barely legal clone that it was created based on reverse engineering.
The mentality is exactly the same for those who want to run illegally dumped roms of their favorite consoles in emulators created by reverse engineering just because companies do not want to get more variants of their consoles or more copies of the games.
It is the same with this, there are alternatives for you to make your fight game from scratch with your own rules but if you insist on using ikemen, you must know that it is nothing more and nothing less than a vitaminated clone from its roots.
You say that in the end the MUGEN engine belongs to the community that made it grow and it is not true, this ikemen engine was made as a way to circumvent the license source code that elecbyte had no desire or obligation to share and you have the freedom to make your own alternative too, unless you were to create something and do not mind that someone arrives and changes here or there and magically another person claims it as his domain.
Apart from everything, you can not or do not want to contribute with anything but money and believe me, no matter how motivational is the money, you do not write or do not think of a code that in the end another will use for free thanks to a permissive license.
You want everything for free, made and stripped so you can use it to your benefit, claiming that it is for the benefit of all, it is a noble thought but with obscure intentions in between.
Some day we will all think about business if it is still interesting and profitable this, but in the meantime please do not continue corrupting this hobby with money, because when there is money involved and things stop being done for the love of art it becomes something ugly, unfunny ,without charm that do not want to be continued more.
If you want to contribute so much and understand that meanwhile there is not a legal way to obtain the original source code in good terms, this is an obscure barelly legal protected by laws reverse engineered copy clone licenced by MIT standards engine, an improvement one of something already existing, owned, claimed and protected from roots.
Plase make that package that you want so much, but for everyone, for the benefit of the whole community, not only for you who need it.
I hope that at last you have understood this legal, mental, emotional and moral barrier that we have, this as you said will be my last reply to you and as I said to you already, take the engine, create your game, sell it, make money and be very happy.