The Financial Accounting Foundation (FAF), a not for profit entity of which the Financial Accounting Standards Board (FASB) is a part, will be charged with maintaining the US GAAP Taxonomy, per the following WebCPA post and FAF press release. When the SEC began funding the US GAAP Taxonomy it originally started at the FAF but was transferred to XBRL US as the progress progressed.
This is an interesting twist. The first thing that came to my mind is the potential switch to International Financial Reporting Standards (IFRS) by US companies. I think there will, at least for the foreseeable future, be a US GAAP Taxonomy going forward if this occurs. The US GAAP taxonomy adds information for many industries, details not found in the IFRS taxonomy, and SEC rules which will never be covered by the IFRS taxonomy.
The fact that the FAF maintains the US GAAP Taxonomy could cause even more "market provided support" for things which make the US GAAP Taxonomy usable by reporting entities. This is similar to the fact that the FAF publishes the accounting standards, but Wiley and others publish books which explain and make the standards easier to use.
Also, the AICPA publishes things like Accounting Trends and Techniques. When this SEC XBRL filing really gets going, I think people will realize that using the US GAAP Taxonomy as the starting point is not the way to go, rather there will be XBRL templates which are better starting points. The end result will be valid XBRL which can be submitted to the SEC. It is just that the market will be able to better decide what is useful.
I do find the timing of the next update interesting:
The FAF and FASB plan to assemble a small team of technical staff who will be dedicated to maintaining the taxonomy and will work towards the release of the next taxonomy update in early 2011.