Yep. Been a long requested feature. One of the reasons why the post states: "This feature also removes the last significant barrier to migrating legacy MySQL applications to PostgreSQL."
Due to the English language however there can be some debate as to what they meant. In this case "legacy" is most likely meant to describe the "MySQL application" not "MySQL" itself.
A meaning that adds something to a sentence is a more likely meaning than one that adds nothing to a sentence. If you take "legacy" to mean "being migrated from" then the sentence becomes
This feature also removes the last significant barrier to migrating being-migrated-from MySQL applications to PostgreSQL.
It's more likely that if "being migrated from" was the intended meaning, they would have simply left the word out.
First, my comment says "more likely" so it isn't assuming anything.
Second, if we change "more likely" to "definitely", the assumption is merely that the sentence in question is written with the same command of the English language as the rest of the announcement, i.e. no egregiously redundant words.
Maybe not a perfect word but very easy to understand in the context.
You definitely have a point, though. How the phrase "legacy X applications" is interpreted likely depends on whether the context is an announcement by a competitor to X.