For my own selfish merry mutant loving reasons, I hope this happens. Can you imagine X-Men movies made by mouse house?! I would cry with joy.
As for Disney not making R movies, I think owning FOX might be a way for Disney to get around that. When you buy Marvel you think happy, shiny comic characters. Nice MCU people. FOX has always been grittier and I think that Disney is smart enough to know that there is a giant cash flow tied into Alien, Deadpool, etc. Not every movie has to be comic related
What concerns me more than anything is the SMALL screen that Disney would stand to possible own. I love a lot of Fox/FX/FXX shows. Those are usually the darker shows. I don't want Disney touching them at all. Could you imagine FARGO watered down?! Always Sunny not being so crass and hysterical?! Let alone what Disney could do if they owned sports show rights. When Disney bought ABC, then grew their tendrils into ESPN - they killed it.
So if this deal goes through, I want Disney to just own MOVIE rights.
Overall, what I think is happening is that Disney is looking to buy more properties so that when they spin off their own stand-alone subscribed service it won't be filled with cartoons and MCU. They want adults in there too.