We did the modification in the HTML Purifier plugin to use the last version of HTML Purifier library. With currently used version of the lib, we had trouble using target attributes for a markups, for example. Can we share this modification with the community ? what is the procedure then ?
Sharing your changes with the community is always appreciated and encouraged.
The first place to go, if you haven't already, would be the developer mailing list. The process for posting and updating addons here on Omeka.org is still not quite up and running, but the dev list is always a good place to start. Also, always feel free to just post about modifications you're making even before you want to release them, to gauge interest and see if anyone else has gone down the same road.
The Purifier plugin has been allowed to stagnate a little bit, as you've noticed. The "far future" version of Omeka has HTMLPurifier built in, and we've been neglecting the plugin for a while (also, we really haven't heard much about it).