I'd add that while yes, you can migrate data from domain "x".com on M1 to domain "y.com" on M2, when it's time to launch, if you had any SEO rankings that you want to try to pass along, you'll need to be very careful about the process.
Chances are that no matter how you do it, you'll lose a portion of the organic search engine rankings that the site had under the original domain. To salvage as much as you can, you'll want to create permanent redirects, do your best to keep the URL structure the same, and flag the Change of Address with services like Google Search Console (Webmaster Tools), along with submitting the new sitemaps, having a proper robots.txt file, etc. etc.
IF the site was making revenue from organic search traffic, I'd recommend being very very cautious about switching domains, especially as part of a launch of a new version of the site. It's often best to switch domains with as few site changes as possible so that search engines can recognize that it's a one-to-one change, and not see it as a new site. From my experience, in the eyes of Google, if it looks like you're redirecting to a new site, your SEO rankings can drop significantly.
Even if things go well, you'll want to keep an eye on Google Search Console for errors and issues, like 404 pages, that should be addressed quickly.
Best of luck!
