You can still open Pre-MP4 replays with the frozen install of MP3 and play against those. They're marked with a exclamation mark on track pages to show they're older replays and won't display properly in MP4. In many cases the maps are updated, but the replays are not.
We do have a backup of all maps the mx crew updated. But we have no plans to make those public, unless an author requests one.
The majority of players have updated to MP4. You shouldn't stay on MP3 unless you have very specific reasons why you need to.
eyebo says:
I'll post here when we're finished.
Oh we finished a long time ago, and I forgot to post here.