demo: yes, there is currently no doom3-scale test level for shiva. nor is for acknex *cough*office.wmp*cough*.
performance: test the car dem (bloom, motion blur, normal mapping, physics, collision, all together) and judge yourself. but it's no 700-3000-fps-irrlicht.
shaders: there is no real shader editor, that means you cannot write your own fx files currently. but that's not necessary. shiva offers a material module where you can "assemble" your shader including variations of normal mapping, env mapping, true reflection and real refraction, the possibilites of combining em all seem endless. again, see the car demo for shaders.