We utilize lighting App pages to display visualforce pages. Currently the only visualforce page that is available in lightning is the Contact_Mobile page which has limited functionality compared to the mkto_si__Contact visualforce page. I would like to see the mkto_si__Contact page to become lightning ready so it can be used in lightning app pages.
Can you check the version of MSI package that is on your SFDC instance ?
If it's lower than 1.4359.2, you should consider upgrading it.
Currently we do have the latest version installed, version 1.4359.2. The reason we would like to have this available for lightning is to display this visualforce page as its own sub-tab under the contact/lead lighting app page instead of just a visualforce section on the details page of the record.
Yes, then you are correct, this is not possible. It would take that MSI is turned into a lightning component, which it is not.