The most crucial new feature needed is built-in reputation management (credence or something similar), with poorly-reputed files preferentially dropped by ultrapeers when they have to dump some search results to not choke and die of insufficient bandwidth. Currently, bogus results are quite frequent and seem to get injected from a lot of places, and though it's easy to spot and ignore them most times or even block the hosts spewing them into the network, they are crowding out legitimate results, a problem that you can't solve by simply ignoring it.