So this says all files will be encrypted with RSA, doesn't that mean who ever wants to access them needs the key? Is this just not a successor to Megaupload then? How will sharing files publicly work? Or will it at all?
It's all in the article. You can either send the recipient the key in a side channel or include it with the link.
You could do that if there is a per-file key. But you'd need some client software to store and manage keys for individual files for easy exporting urls including these keys, and I read that MEGA is managed only via web (at least now).
This is built in as I understand it, there is a master key that is used to encrypt a key database that is stored on the server for each user.