Google recently announced that they were retiring support for OAI-PMH in Sitemaps:
We’ve found that the information we gain from our support of OAI-PMH is disproportional to the amount of resources required to support it. Fewer than 200 sites are using OAI-PMH for Google Sitemaps at the moment.
Amen. As someone who once implemented an OAI-PMH service I can say that the web does it what it needs to do quite well without overblown standards. Committee-based ham-fisted over-architectures have their place, the dustbin of history.