The Pentaho Data Integration (PDI) Marketplace is a great place to share your PDI/Kettle contributions with the community at-large. To add your plugin, you can pull down the marketplace.xml file (via our GitHub repo) and add your own entry, then submit a pull-request to have the entry added to the master Marketplace.
But did you know you could 'host' your own PDI Marketplace? The Marketplace is designed to read in locations of marketplaces from anywhere you like, via a file at $KETTLE_HOME/.kettle/marketplaces.xml (where KETTLE_HOME can be your PDI/Kettle install directory and/or your user's home directory). Here's an example file on Gist.
The file contains a list of marketplace entries, which are locations of various lists (aka marketplaces) of PDI plugins. The URLs provided are used to read Marketplace XML files, which contain the PDI Marketplace entries.
This is how I test incoming pull-requests for PDI Marketplace plugins. I use the marketplaces.xml file from the Gist link above, then checkout the pull-request from GitHub. Then I start PDI, go to the Marketplace, find the proposed plugin, try to install, open the dialog (if appropriate), then uninstall (NOTE: reboots are required). Of course, support for the plugin itself is (perhaps) available via the submitter. These details are available in the PDI Marketplace UI before installation, and all licensing, usage, etc. is provided by the submitter.
The benefit of having a marketplaces.xml is that you can decide the list of PDI plugins available for download. If your clients have a marketplaces.xml that only point at your own repositories / locations for plugins, then you can control which plugins can be downloaded by those clients. For developers (as I show above), you can use it for testing before submitting your pull-request. For consultants / OEMs, you can decide which plugins should show up in the list. This mechanism is very flexible and should support most use cases.
In closing, I personally review many of the PDI Marketplace entries (aka pull-requests in GitHub), please let me know if you have any issues with announcing your plugin or otherwise contributing to our community.