The main issue I have is with the overall structure of this section. The use of the `try..except`, the private method, and the projection-specific logic (some of which you inherited) all suggest the code is in the wrong place.

I think it would be better if the `InterProjectionTransform` class knew nothing of `_CylindricalProjections` or `PlateCarree` projections. Instead, it should enquire of its projection "Do I really need to transform these vertices? If not, should I use some simple alternative coordinate values instead?".

For example:
```
bypass_vertices = self.source_projection.can_bypass(self.target_projection, src_path.vertices)
if bypass_vertices is not None:
    if bypass_vertices is not src_path.vertices:
        src_path = mpath.Path(bypass_vertices, src_path.codes)
    return src_path
```