MCW10E is not going to be replacing the java client. MCW10E is meant to be just like pocket edition, designed to be ran on windows 10 phones and tablets. Phones and tablets don't have the power that a PC has, therefore they would not use MCW10E as the PC version, because they would have to keep it as light as possible to run on mobile devices. I highly doubt they will recreate minecraft in C++, they have put too much time into making the current client to throw that away and remake it. Microsoft also know that the community likes the game as it is, and re-making the game would destroy a lot of the larger communities (Forge modding, whats left of the bukkit community, sponge, loss of modding = no plugins = servers begin to die). If they were to implement their own modding API, it would most likely end up being "make a DLL, compile it and throw it in" therefore it would need to be a .NET language. A lot of current modders are professional java developers or just learned java to make a mod. Therefore they would either have to learn a .NET language or stop modding. There are other examples of how this would f*** things up, but long story short, it ain't gonna happen. We will most likely see a large update cleaning up the inefficiencies and bugs that notch has left in since he started the game (because he is an idiot) however, and we may see them change to a different implementation of other graphics libraries to bring the quality of the game up to scratch.