I don't know what needs changing in null sec. I'm sure that sovereignty has it's problems, along with the logistics of managing large alliances.

However, as far as for the solo player, null sec as it is is fairly optimal IMO. At least it's fun for me to explore null whenever I get in the mood. It's also fairly sparsely populated in some regions, and this alone makes it very penetrable for the solo player who wants to make isk out there. The biggest thing that I can think of to make null sec more penetrable for the solo player is, as I've mentioned numerous, numerous time, would be a ship somewhat like an orca that can serve as a mobile platform for a player or two. Simply set up the ship like a station in a system that has limited capabilities for manufacturing, clones, etc., and also make it so that it consumes fuel at a rate that requires it to be refueled every few days, and require that it be refueled at a full station and boom, we have a pretty cool new ship that lets the solo player live out in null sec for a low investment for limited periods of time.

As far as PvP goes, I'm not sure what could be done there. People complain about blobs in null all the time, and this is simply going to be the reality of null sec so long as we have large alliances which live in null and have incredible reserves of materials and isk. I'm not saying that there can't be improvements to null to make small gang PvP also a worthwhile form of PvP, but I am saying that you're not likely going to get rid of blobs. One idea would be to move away from POS's and stations (or at least provide options for smaller groups of players) in null where the industrial strength or an alliance needs to be fairly centralized in a given system at a POS or station, where both are pretty difficult to attack with a small gang of sub-cap ships, which would encourage alliances to spread out military forces more in order to defend targets that are more spread out.