Hello @Paul
I heard back from the team on your question and their response confirms what @Michael Koerner said above: Enterprise Integration Tool for Visual Studio 2019 is not at a priority on the roadmap at this time. Formal guidance from the team is to use BizTalk Server Visual Studio tools for the time being as they're equally capable and more with regards to schema, mapping and flat files etc.. I hope this brings a bit more clarity.
If you feel strongly about the importance and priority of the EIT for VS2019, please consider submitting a feature request on Azure UserVoice for Logic Apps or upvote an existing one for the team to review further and consider for future roadmap.