So why not just use Google Drive (or dropbox)?
I feel with features like secure file sharing (though only with other ppl with google accounts), reasonably good security[1] and Inactive Account Manager[2] it should work for legal docs. Especially considering Google is going to be around for a while.
I would rather use a Mozilla offering but they don't really have too many things for regular consumers outside of firefox and send.
[1]: https://myaccount.google.com/security [2]: https://support.google.com/accounts/answer/3036546?hl=en