Hi,
There is no definitive answer as yet, but from the information that is publicly available, I would expect from previous experience that although you will be able to implement a CRM2011 OnPrem deployment you will only be able to use CRM2013 via a new Dynamics CRM Online deployment.
Existing deployments that are purchased now will be able delay their upgrade until the start of Feb 2014 at the latest ( based on the options presented to you when you use the 'reschedule' link within Dynamics CRM Online at the moment, but this could change).
Donna has brought together the best resources for CRM2013 - edwardsdna.wordpress.com/.../getting-ready-for-crm-2013
hth,
Scott