(Low effort comment) I wonder if this means OSMAnd and OrganicMaps will now finally team up to deliver the ultimate FOSS Map app

Both apps mainly use downloaded/"offline" preprocessed map data in their own formats.

MVT format vector tiles are not remotely suitable for navigation or search (not ruling out that something could be hobbled together, but it would be a bit of a stretch).

There can be no one ultimate map app because use cases differ. For example, OSMAnd has many power-user features that are very useful for people who also contribute to OSM, but would only clutter the interface of an app for normies.

At the very least I hope it means they can share map tiles between them so I don't have to use gigabytes of space on the same map

There is Organic Maps already.

How so?