Quote: "However it's is a lot of work, just for cube map reflection, I would be much happier with simple cube mapping and additional gloss texture slot on a new shader"
Indeed this could be achieved , and provide better graphics than actual ones.
Probes or the cheap system you mentionned, allow you to have less or more reflective surfaces, you can simulate lot of materials with lot better fidelity than simply using a specular value. You'll be able to get some rubber with alsmot no reflection, rought metal with little reflection, or polished metal surfaces with almost full reflection. This can be used for wet and water textures surfaces.
You'll make better GG looking games.
Quote: "
the performance costs are quite significant for realtime"
There is recent adoptions for Forward rendering + because of VR , instead of Deffered that costs more GPU.
Gamers average PC are not very old, those who plays actual and past games must be using hardware 5 years old maximum that already could perform well. Today you can get good old graphics card for 100$ performing great.
One thing to blame won't be the renderer but the 3D engine optimisations.
The roughness simulates better light absorption, this is the advantage over old rendering systems.
With specular only metal materials will have the old look, with reflections it will look more like real metal.
img]http://blog.playcanvas.com/wp-content/uploads/2014/12/shadingComparison2.jpg[/img]
Lightmapper is not producing good bouncing lightening, it looks very dated, that's why it is better to aboid using it in GG i think, because it will override all your lighting effects.
