The main obstacle to do such a thing right now is that the HTML of the questions is still generated from core.
So if you want to get rid off bootstrap, you must rewrite the HTML via JavaScript.
In LS3, we'll provide a system to change the HTML of a question ("question template"). We'll provide it question type by question type, with each LS3 release (3.1, 3.2, etc).
At the end of that process, when all the question types will have been converted to twig, it will be possible to use limeSurvey to render only json + the EM scripts. So you'll can do what ever you want, like using foundation, viewjs or react.
Note that the template and sample survey were adjusted at the old Limesurvey v2.06 version so it may not wokr with newer Limesurvey versions.
Anyway, creating the exact same layout requires some efforts for customizing the template. Best ping the OfflineSurveys sales team for a quote: sales@offlinesurveys.com
Best regards/Beste Grüße,
Dr. Marcel Minke Need Help? We offer professional Limesurvey support:
survey-consulting.com Contact: marcel.minke(at)survey-consulting.com