The philosophy articles on Wikipedia are not very good (to put it mildly), and to fix them would be a tedious, unrewarding process that could be completely undone by anyone with a web browser.
On the other hand, the SEP is (a) fantastic, but (b) necessarily slow to expand its content. I say necessarily slow because the SEP expands its content by getting people with a very high level of expertise to write in-depth articles that are edited and revised. That's why the articles are good. So, while the output is excellent, the process by which it gets that output is fairly time/energy/labor intensive, and the only time/energy eligible to be used comes from a relatively small set of people (those with high levels of expertise). To sum up: By taking large amount of time and energy from a very restricted group of people, excellent, detailed articles can be (and in fact, are) produced.
While that process works really well for the goals of the SEP, there are other processes which, while not well-suited to producing the same sort of content as the SEP, are good for producing a different sort of content.
The goal for the site that I am starting is to produce a site that complements existing resources like the SEP. Instead of shooting for articles which cover a given topic in great depth and detail, this site would aim for articles that give broader, shallower summaries. Rather than having a single author for each article, it will allow individuals to make small contributions to articles. Both of these changes will lower the bar for what level of expertise is required to be able to contribute.
Additionally, it won't be limited to just articles on articles on philosophical topics or views. It will also (ideally) present articles on organizations for philosophers, recurring conferences, various philosophy journals, etc. Perhaps even articles on philosophy departments (sticking to bare-bones information like the size of the program, faculty lists, associated conferences, journals, reading groups, etc.) and individual philosophers (again sticking to barebones facts like where they are located, what their active research areas are, etc.).
The great thing is that pretty much any philosophy graduate student or professor of philosophy is in a position to make some valuable contributions to this sort of project, and making such contributions won't necessarily require a substantial commitment of time and energy.
So, if you want to get involved, contact me (lmpowell at usc dot edu). In order to contribute, you will need to register an account. Registration is limited (roughly) to philosophy graduate students or professors (i.e. people actively involved in academic philosophy).