Ok so there are a huge amount of rumors, and guess what? 90% of them are fake.
You can play with more than 7 people, xbox live is not required but is required to play with xbox one players, this is not minecraft pocket edition, it is based on the same principal of using c++ instead of java, the only reason it is an "exclusive" is because its completely recoded from the ground up, once its out of beta I'm sure it will be ported to other operating systems, and modding is not supported at the moment, but give it some time and mods will start to show up just like Minecraft Indev and Alpha.
You guys would not believe how many damn articles I had to go through to get actual credible answers about this, because at first I though it was going to replace the desktop version ( That it kind of is supposed to considering its going to be a modern app and not a win32 program) but yeah, its just more rumors that are spread from people who hate Microsoft.
I don't make stuff up, so if you want to believe, good for you, if not well I can't change everybody's mind.
Also for anyone wondering the reason it works better than the java version is because the java version is incredibly un-optimized and this is a C++ Modern App built from the ground up.