I'm coming to Mapillary from the late great Microsoft Photosynth.
Photosynth had no requirement for one's images to have lat/long coordinates for each image.
Rather, since they were using structure from motion techniques (as Mapillary now does) to solve the relative positions of the photos to each other, Photosynth would find the photos' relative camera positions to each other and then allow me to rotate and scale the point cloud generated by my photos to fit the map.
That approach allows me to essentially make sure that my beginning and ending photo positions are correct and let all photos in between be automatically pulled into place.
I'm currently finishing my first Mapillary upload and was somewhat horrified that I had to drag each individual photo onto the map prior to upload (since my camera does not have a GPS on board).
I do understand that this site is all about geopositioning each image (and I applaud that) however I know from experience that the workflow of using images without GPS coordinates can be greatly simplified by solving the relative camera poses first and then aligning the entire group to the map.
Anyway, this is a pretty high priority for me in terms of whether Mapillary is going to be usable for me. I certainly don't want to have to manually drag and drop hundreds of thousands of photos onto the map one by one and manually input the compass bearing for each one.
I know Mapillary uses OpenSfM, so you could do something just as usable as Photosynth with regards to mass aligning photos to the map. I'm just trying to make sense of your input workflow.
In the meantime, if anyone out there knows if one of the mainstream Structure from Motion/photogrammetry tools out there (VisualSfM, PhotoScan, ReCap 360, RealityCapture, Acute 3D Context Capture, etc.) has the ability to align one's photos' point cloud to a map and write the resulting GPS coordinates back to the source photos so that I could give them all an estimated GPS location prior to handing them off to Mapillary, I would appreciate a walkthrough on how to make that happen,