Hey there -
What a great question! It's definitely a very involved one and not a decision to be taken lightly. In fact, I was just having a similar conversation with a group of people recently when one of them posed it as well.
First of all, let me make a few comments around Domain Authority and how you should be thinking about it. Domain Authority is a metric created by Moz that correlates to how likely a website is to rank. That said, it's still unclear how the search engines are treating subdomains as they can be on different servers, be completely different technologies, and targeted to different countries as you well know.
That said, I am always a fan of consolidating link equity. If you move from a ccTLD to a country-specific subdomain and do all of the permanent redirects correctly, two things will likely happen:
- You will consolidate link equity from many different domains to your one overall domain, which should help with rankings/traffic
- You can consolidate your brand, which may help with conversions.
That said, you need to do your customer research and see if they'll trust eg france.site.com as much as they trust site.fr. There are definitely ways to make country-specific subdomains work very well for SEO, but this migration should not be done solely for SEO reasons in my opinion.
Hope that helps.
John