This might not be as impressive as you are expecting. Since we have all the source assets, the peg viewer simply tells us what is in the peg, file sizes, and offsets. It isn't a way to view the peg content itself. That is not a hard tool to write though if you were so inclined. I'm telling you this now so you can start work on such a tool if that is what you want. The peg file format is out in the forums now.
As a side note here, I'm really excited to see what tools the community makes. We will release tools that we use and some new ones made just for modding, but please keep in mind that our workflow is different from yours so these tools may not be ideal. I would hope that you guys take up the challenge and use the information available to make amazing things. Initially I'm sure there will be a lot of batch files created to join together common tools used in a workflow, but I'm most excited about the applications that will be coming that will either do the work themselves or shell out to our tools. These applications will really open the game up for people without as much technical knowledge and the more mods the better, if you ask me.
I'm not trying to set you guys up for disappointment here, I'm just interested to see what will blossom from the community's endeavors and that doesn't end with content.