Since I use Unity quite a bit and am excited about anything that improves the Houdini Unity pipeline, can anyone explain the significance of this update in 16.0.762
Now supporting 32-bit index buffers for mesh generation on Unity 2017.3+

Here's the Unity 2017.3 beta documentation [docs.unity3d.com] on the mesh index type.

Here is a discussion about it [forum.unity.com] on the Unity Forum.

32-bit should be great.

Desktop OpenGL GPUs have always supported 32b indexing. Indexing allows you to have a array of points and connect them together to form primitives (triangles, lines) in arbitrary order. Indices are always unsigned, and you can use uint8 (up to 255 points connected), uint16 (up to 65535 points connected) or uint32 (4 billion points connected, effectively unlimited) values to represent the indices.

What this means for Unity is that meshes no longer need to be diced up into ~22k triangle batches. It's still a good idea to keep them in reasonably sized batches (<1M), or even desktop GPUs can start choking, but the low batch size that Unity used to support could cause a lot more draw calls on desktop platforms than was really necessary.