To my knowledge, Jolla have not explicitly stated what architecture they will use in their handsets.
Given that the core os has builds for both arm and x86, either could present as an option.
HTML5 may still present as an option through qt webkit and there may be a strategic reason for the 2013 release target if there is a plan to provide application compatibility with the likes of BB10 which will release around the same time.
It owuld be interesting to see if the android compatibility layer that is planned for QNX/BB10 could be ported across to Mer.