Implement custom vertex attribute
The current S3DVertex only allows BiTangent, BoneID, BoneWeights, Color, Normal, Position per-vertex attributes and doesn't allow people using Saga3D to extend and possibly add more data per vertex. Although you can pack it into the the attributes you don't need like BoneWeights it doesn't seem like a solution then more of a quick hack.Extending either meshbuffer or S3DVertex to allow users to set attributes and their sizes by themselves will allow for more capabilities in terms of what they can add without workarounds or hacks.
etc: Particle system having custom per-vertex attributes defined: https://github.com/danginsburg/opengles3-book/blob/66df74e1cea9a2103063c84f1a52049b54ab75b8/Chapter_14/ParticleSystem/ParticleSystem.c#L113
Examples: (Pseudocode, probably not good ways to tackle this):
VertexDesc desc;
desc.setLayout(0, float3); //pos
desc.setLayout(0, float3); // color
Vertex vertex(desc);
vertex.set(0, FOOBAR);
vertex.set(1, FOOBAR);
Thanks!