We've split up our landing page enhancements into two phases. The first will allow marketers to build a mobile view of their landing pages using our existing WYSIWYG landing page editor. This is entering beta and is on-track for general release in January. If you're interested in participating in the beta, please email me.
The second part of the project will enable marketers to build and edit truly reponsive landing pages (what I call "fluid" pages). The editor will be user-friendly so that you won't need HTML/CSS skills to edit these pages. We'll be providing some pre-built templates to start from, or if you've written the code yourself we'll have a simple way to import it into Marketo so that your marketing team can leverage it with ease. While I don't have an ETA for general release at the moment, we're on track to have this in beta toward the end of Q1 2015.
Thanks for being patient and stay tuned for more updates!