Could analytics be used to store central cloud data e.g. Leaderboard, that could be used within a game?
Not really. In the first place, analytics data isn’t designed to be handed back to the user as you’d want for a leaderboard. Also, data is aggregated to avoid revealing the type of user-specific info you’d want. What you need is a server. Cloud DB (which is still in alpha) might be an option if you’re not prepared to build your own. Or something like Parse.
Any feature you’d like to see, you can always vote for here: http://feedback.unity3d.com/forums/unity/suggestions?utf8=✓&status=0&category=analytics&view=hottest