Does Deployer support publishing themes to WordPress.org?
No. Theme publishing on WordPress.org has a different process, that is not based on SVN - you have to upload .zip files there.
Can Deployer submit a new plugin to WordPress.org?
No. You have to manually submit your plugin here for review. Deployer only works with plugins that already have their WordPress.org site.
Can Deployer convert from readme.md to readme.txt
No. WordPress uses a custom format for their
readme.txt file. If you want your plugin to look nice on both GitHub and WordPress.org, you have to have both a
readme.md (in Markdown, for GitHub) and
readme.txt (for WordPress.org) files.