It's not possible, as Oxwall isn't using a template system like Wordpress or other CMS. Oxwall generates the site templates and you can't change the classes and everything. Well, that's not true! You can change them, but then you have to change core files, which is a lot of work and you have to do it after every update oxwall releases again. Theming in oxwall is like it was in the late 90s. It's complicated, it's confusing, it's not or not well documented and it is old school. Instead of giving you functions or an API, oxwall throws everything at you and tells you to eat it or to die from it.
That's the reason you mostly find themes, which look like the standard themes, only that the colours have been changed. There're no total conversions or anything. If you want it to be reponsive, then you have to use the classes and ids available.
So, there never will be a bootstrap theme, except the devs add it to the core or they change their template system to modern standards.