Will be there some kind profile aggregation/central page for all StackExchange sites?
Where I can see all my reputation score, stats, badges, replies etc...
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There already is, assuming all your accounts are associated.
You can get to this page through any of your user profiles, and going to the "accounts" tab on the right side.
Note: this will only show StackExchange 2.0 sites, not the original StackExchange sites. I don't think there will ever be such a page for the latter as they are completely dissociated with the new sites.
Re the question edit: Check out this application over on StackApps.
Stack Exchange Network Profiles