For a website we were building we were looking for solution to insert an address within the content of a page. This address needed to be selected from a database so when the address itself changed, it was automatically updated within the content of the webpage. This functionality is often called a placeholder. To be able to build this functionality we had to make a plugin for the wysiwyg editor.
After having a closer look at Kupu we came to the conclusion it is possible to create a plugin for Kupu but, it is really hard to separate your plugin code from the Kupu codebase. The last thing we want is to edit the source of another product since this will most likely create issues when upgrading to a newer version of Kupu. We also had a look at the FCKEditor plugin for Plone but this editor also isn't very plugin friendly.
When examining the TinyMCE codebase we noticed TinyMCE is by itself already fully based on modules. This made it really easy to create a separate TinyMCE plugin in another Plone product. The only problem at the time was that, as stated above, the development of TinyMCE was put on halt. That is why we decided to upgrade the product ourself to the newest version of TinyMCE and Plone. After that we also added a control panel to make it easier to configure the editor.
At the moment we are working on the placeholder product for TinyMCE which should be done this summer.