It’s important to think about platforms and ecosystems together as platforms by themselves aren’t useful unless someone is using them.
The term platform is thrown around in product marketing material to the point that its requires further definition. I like Bill Gates’s take: “A platform is when the economic value of everybody that uses it, exceeds the value of the company that creates it”. Ben Thompson offers a great post with more on this definition in
Legacy platforms imply that there is a new platform on the table or at least on the horizon. It’s first worth the effort to diagnose the problems with the existing stack