Well, yeah... there was a whole different architecture for Moodle v1.9 and v2... As well, as I understand it, few of the third-party plugins for v1.9 are being adapted to v2. For most of them, the original author and/or maintainer is not interested in continuing, and Moodle.org does not have the human resources to be able to assign a team to rewrite these plugins.
If you are looking at replicating an existing plugin, then you may be able to use the existing v1.9 code. Better contact the author and get permission to do so, but if you cannot make any contact, then best to ask, perhaps you can be listed as the assigned maintainer.
If you are looking at writing your own, you may need to be able to provide the provenance for that plugin. (That is, original proposal, original outline, early models and development pathways etc.)
In either case, you may want to start here, using the guidelines to make your module.
There is a list in the Moodle Tracker of useful modules that need to be updated. Good luck..