Sometimes it's great to look at what other tools are cooking and I've recently got curious how the live2D stuff works and done some digging. I found some functionalities that I think could be really interesting for Construct so I made a wishlist.
1. Mesh setup
Meshes can be set initially without deforming the sprite. That allows the base-mesh to conform to the actual content of the sprite instead of always covering the entire sprite rectangle. From what I gathered this might give better results when deforming the sprite, in particular if the initial sprite has some curve to it. If the mesh follows that curve initially, deforming it should lead to cleaner deformation.
They also have an automatic function to create this mesh. docs.live2d.com/en/cubism-editor-manual/mesh-edit which of course would be nice to have. But even being able to deform the initial mesh manually to fit the sprites texture would be a great starting point.
2. Clipping mask
It's super easy to create a clipping mask for any kind of masking purposes. Take the sprite you wanna clip, reference the sprite that should be used as clipping mask. Done.
docs.live2d.com/en/cubism-editor-manual/clipping-mask
docs.live2d.com/en/cubism-editor-manual/invert-mask
In Construct we have to use blend modes (destination out etc.) which becomes increasingly complicated if you wanna have multiple objects that are cropped because the destination out applies to everything below. So when cropped objects overlap the clipping mask from the top sprite also crops the bottom sprite. Effectively you need to put every single pair of object and clipping mask on their own layer with force own texture.
Mind you this is quite a highly requested feature already: github.com/Scirra/Construct-feature-requests/issues/726 although the solution skymen proposes is slightly different.
3. Deform Path
One can define deform paths which can be used to manipulate the underlying mesh. Instead of having to manipulate all the individual points of the mesh, this path works kinda like a classic bone/joint. It simplifies adjusting meshes a lot.
docs.live2d.com/en/cubism-editor-manual/deformpath
A similar application would be puppet warp which is available in various tools: tips.clip-studio.com/en-us/articles/10496
These are already really useful during editing since right now you must drag mesh points 1 by 1, but I'd imagine these paths could be manipulated at runtime too, allowing much more convenient manipulation of meshes at runtime (which is currently easily the most cumbersome part).
3.1 Soft selection
On a sidenote for editing meshes, a soft selection option would be great. github.com/Scirra/Construct-feature-requests/issues/789
4. Blendshapes
docs.live2d.com/en/cubism-editor-manual/blend-shape
The ability to blend between two (or more!) meshes. This is often used in 3D for facial expressions. You take a copy of your base-mesh, deform it to e.g. make the character smile and add that as a blendshape. Now you get a slider on your sprite which allows you to set how strong the deformation is applied and you can make your character smile between 0 and 100% (sometimes it even possible to extrapolate in either direction). Now you make another blendshape with mouth open, which allows you to mix the smile and the open mouth. Of course this can be used for all kinds of animation purposes, not just facial expressions.
github.com/Scirra/Construct-feature-requests/issues/787
While typing this timelines popped into my mind, which could maybe be used to set this up... except they don't appear to support/track mesh deformations. So there goes that. (Unless I'm mistaken)
5. Deform Path physics
This is kind of an optional thing but would be cool regardless. One can set up a physics calculation, which is then applied to a deform path. I'm assuming they are using some kind of verlet physics here.
docs.live2d.com/en/cubism-editor-manual/physical-operation-setting
This could be cool to make a character with a dynamically animated tail, cape or hair. Or really anything you can think of. I actually made a cape with this method before, where I used verlet physics to simulate a rope attached to the character and then used the IRenderer to render a mesh. But I couldn't get further than rendering a solid colored cape. I'm assuming it's possible to actually attach a texture if you actually know what you're doing (unlike me).
If I had to prioritize:
1. Clipping Mask ("simple" feature, big payoff)
2. Mesh setup (I'm assuming the Deform path will not work as well without this so this has to come first)
3. Mesh soft selection
4. Deform path (Easier mesh manipulation both in the editor and runtime)
5. Blendshapes (An alternate way of deforming meshes at runtime, probably a bit more niche than deform paths)
6. Deform path physics