Passing form data from Wordpress to CiviCRM

Our customer Werk Met Zin (platform of independent 'job' coaches and trainers in Flanders) use a Wordpress site as a front end and CiviCRM as their back end. There is now one specific instance where an individual can apply for a series of coaching sessions on the website. This has to be passed to CiviCRM and rather than updating the website to Drupal we are passing the data from the Wordpress site to CiviCRM. The company that develops the Wordpress website knows nothing about CiviCRM (and want to keep it that way.) Any remarks and/or suggestions are very welcome, and obiously we will share the solution with the CiviCRM community once it is complete. Here is what we plan to do (and thank you to Werk Met Zin for funding the development and us at CiviCooP for developing.....):

• create a Wordpress plugin that catches the form (with the save_post action) and passes all the data fields on the form to CiviCRM using the REST API WpCivi (entity) Submit (action)
• create a CiviCRM native extension with the API WpCivi Submit. In this extension we will:
  • check if a contact exists already and create one if it does not
  • generate a special activity for the contact with custom data for the information entered on the Wordpress form.