I like your vision for Hypen and I sincerely hope that you can avoid the faith of every project that tried it before you! (all the toolkits that started as declarative, with clear logic/ui separation, eventually and inevitably add scripting and reinvent js/html).
That made me chuckle though:
Accessibility and i18n tooling:
This is in the plan - accessibility should be the easier one, with i18n tooling coming as more "platform calls" support comes online.
In my experience accessibility is far more difficult to get right, but maybe I've just been unlucky. :)