In general IP address for peer ID is a bad idea.  For example, running over tor, proxies, running with IPv6 (eventually) when IPs will be quite plentiful and could essentially be switched every hour or whatever etc.  IDs in a p2p system without a central authority are problematic.   ;-)

As far as IDs, check out what DannyHamilton said, and take a look at the bitcoin paper pdf he linked to.  There are a lot of technical details you'll discover.  There is a lot to read and absorb to understand how bitcoin works and why some changes would be unlikely to occur in anything but an alt.