Version 5 supports step models. I think the format has not changed. I guess the v5 3D model names may have changed to match the official v5 footprint names, not sure.
Anyway, your v4 3d .wrl models are valid as far as you edit your footprints to point to them.
We increased the quality requirements for 3d models. Now only models that are valid for mechanical cad integration are allowed. This means a lot of wrl only models have not been copied over to the new repo. (We now require a step model for every contribution.)
We also require that the wrl files are scaled correctly such that the footprint can use 1:1:1 scaling. This later requirement means that no old model is compatible with new footprints.
This has nothing to do with a format change. It is a change in policy.
The old models will still work with kicad version 5. But not with the new footprints as we changed their name and we set the scaling factor to 1 instead of 1/2.54. (Again the restriction is a policy decision. If you really want you could setup the footprints to work with the old models again.)
yeah, the old 3d models will show up, however scaling is way off. and even trying to rescale the old models to fit the current footprint landing pads from within KiCad itself wont appear correct. for instance the TO-220-3 isnt in the new 3d repo, trying to add the old one by renaming it to work. the leads dont line up with holes.