I think it’s a good idea to reduce the complexity for an average API user. Learning OpenEMS takes some time and there are lot of things to learn. One of the many points to learn is how to read/write a channel and to understand the meaning of the various channel metadata. Just to recognize later that you do not need all the “complexity”. Because in most cases you simply want to set/get values.
I personally would prefer getter/setter methods with Value-Objects. A Java programmer will almost immediately understand it. Also the Value-Object helps improving the readability of the Code which works with the Nature interfaces.
As you already wrote, this change has a big impact on many other things. But on the other hand, it will help especially programmers which are starting with OpenEMS. So I would suggest doing it.