Alphakill

About that alpha on texture feature does it have any name?

Texture alpha kill I think. This is a rather low level functionnality that doesn't really increase shader expressive power.

Does RSX support destination alpha test or any exotic blending modes that require programmable blending with texture barrier to emulate like say PS2, PSP ,GC and even Saturn?

No.

Does it support alpha to coverage?

Yes.

I'm not sure I understand about that per camera function is that something related to the viewport?

Not really.
Triangles from vertex shader can be either "front facing" or "back facing". Usually back facing triangle are culled since they're assumed to be unviewable.
However it's possible to disable back facing triangle culling.

Stencil functionnality have several parameters like mask, opcode for zfail, zpass, fail, and function.
RSX allows to set different parameters for front and back facing triangle. D3D12 on the other hand allows only a couple of parameters to be different.

Does RSX still have register combiners in addition to shaders or was that already removed and finally does it support tessellation since I know Xenos does.

No and no.

1. So I get from this that RSX has some stencil buffer features not supported by modern PC gpus? Can it use early Z or Stencil rejection/test? Are depth and stencil buffers in RSX combined or still separate?
2. How do you emulate triangle fans in D3D12. Triangle fans were deprecated in D3D10.
3. What is the highest MSAA level supported by RSX and does it support SSAA as well or just MSAA? I guess 4xMSAA but it was too weak so games probably used 2x only at best.
4. Have you emulated mipmapping and LOD already and do you directly emulate RSX texture cache? Is texture caching crucial for accuracy of PS3 emulation like it is for example for PS2 emulation(PCSX2 has many errors and unemulated functions like mipmapping due to botched texture cache design)?
5. How difficult do you think it would be to emulate modern tile-based deferred renderer like Power VR SGX543 in PS Vita or even Pica200(it has combination of vertex shaders and fixed functions) in 3DS compared to RSX?
6. I noticed rpcs3 has LLE mode now. Do you emulate Cell and RSX at the register level?