Issues with pointing domain to sub-directory?

What are the main issues to look for if I update my htaccess file to have my main domain point to sub directory that has a new concrete 5 web site install. I am using pretty urls.

It is a redesign of a current site that can’t be offline very long, so I’d prefer to go this route vs. reinstalling and copying everything over to the main directory, but want to go the best route.