Why would it not tie in with the cultures as we currently have them? Like everything else it would be nice if the civics were later than the culture on the tech tree, but I have found times where I have not been able to build an ancient culture until the Renaissance, so maybe as long as the civic is somewhat useful in later times it would still work.
Edit I misread that, I thought it was additional civics based on culture (which would have display issues as well) not replacing or varying existing civics. No

consumed yet this morning

. Ones based on teh original cultural group would work, until we make that optional and choosable as "Cultural heritage"