Images in sitemap

Google just recently has allowed images to be explicitly referenced in sitemaps:

https://googlewebmastercentral.blogspot.com/2010/04/adding-images-to-your-sitemaps.html

I’m wondering if this in integrated into XML sitemap plugin, or if there are plans to integrate this. On my site I don’t actually have images within the post, but I do have a thumbnail for each post which shows on the homepage. If I could include that thumbnail within the sitemap entry for that post it might be helpful.

Thanks kindly!
Dave