Interviewed MD/PhD last year, applying MD-only this year. How the MD/PhD interview worked last year was that you did the MD-only interview on one day (faculty, student, MMI) and then you interviewed with members of the MD/PhD committee on a separate day (my MD interview was in October and my MD/PhD in August). Some of the MD/PhD applicants were then invited to a campus visit (Erring on the side of caution with this one because not all of the students who got emails regarding these visits were not scheduled for one in the end).
Something to keep in mind of well: your application (if its the same case as last year) will be in a separate pool from the MD-only applicants. You are not considered for MD acceptance until acceptances have been determined for MD/PhD. It could be up until March before your application gets released for MD-only consideration if you get rejected from MD/PhD, and at that point, you will most likely get on the waitlist that late in the cycle. I never ended up getting off the waitlist (slightly stung considering Wayne was my only interview), but thats not to say other MD/PhD rejected candidates won’t either.