If bedrock was as moddable as java, I think most of us would have moved there. Chances are there will be no modding scene for bedrock, though. Three simple reasons:
C++ is easier to mess up in. There's no GC and it doesn't protect you from your stupidity
Java is easy. If you go to any snob tech forum they will say it's for people who don't know how to code.
Secondly, bytecode transformations and class-loading.. C++ Compiles to native code, and as far as i am aware there are no libraries like ASM for modifying the already compiled code. Also, class loading could potentially be an issue.
Readability.. Java is inherently quite an easy language to just zip through the file and read or recompile, with C++, good luck.