I think there is a growing sentiment that people do not want to fork Wikipedia to create Wikispecies. This makes a lot of sense. However, there is something important that is needed for Wikispecies which Wikipedia does not provide: efficient access of tabular data.
Think of what we would want to be able to do with Wikispecies. Yes, the simplest of them could be handled by categories, and taxoboxes are a kludgy solution to some of the data input, but now what if I want a list of all endangered species in the phylum chordata? There's just no efficient way to get that information from Wikipedia, even if I have access to the entire database dump.
It is possible that Wikipedia could adapt to handle this type of data, but this is a somewhat fundamental shift in the concept of a wiki. We would essentially need an open access database, where even the table structure itself can be modified, complete with a history mechanism which can somehow allow us to revert poorly thought changes.
There is another benefit to Wikispecies, and it is the same thing we're seeing with the proposal of Wikicommons. Species classification information is largely language-neutral. It would be nice if we could somehow have a single database for all this information, and simply use it on the language-specific pages. Once again, this could be done within Wikipedia though, and this change would be somewhat less of a fundamental shift. In essence, we would simply move the taxoboxes to a common database, in latin, and translate into the local language on the fly (regnum->kingdom, etc.). There is a bit of coding involved here, but once Wikicommons is properly set up a lot of it will already be done.
In the end, I'm opposed to creating a Wikispecies, at least as a Wikimedia project. I think our efforts are better focussed on creating a system which can incorporate Wikispecies, Wikipeople, and all the other wikiprojects together under one roof. I think there are a lot of steps along the way, and Wikicommons is probably the logical first one.
Anthony