I have lots of experience with CMS and have also contributed to a CMS and still do QA. Yes, Sir it is a very important decision unless you give your users a very easy way to replace it for the front- and backend. People really often come and want to extend things in the backend, that leasds to customizations and some companies prefer white-labeled CMS's.
If my goal is to build a great CMS for Rails, does it ultimately matter if I chose to use a Start Bootstrap template for my views?