> Now, the question is... _s and _k should NEVER should appear ?

Yes. They only disappear if Pier can guarantee  correctness. Currently
this is only done for views, but in the future I will add a protocol
that arbitrary commands can request clean URLs.

Also there is currently an issue with the second request that alway
has _s and _k, even if this is not always necessary. Again this is
about ensuring correctness and might disappear in the future.

Cheers,
Lukas

-- 
Lukas Renggli
http://www.lukas-renggli.ch