The only lens that I'm really waiting for to complete my lens collection (aka 'lens arsenal') is a 50mm prime.
1) wide open aperture of f/2 or faster
2) IQ wide open - sharpness, contrast, vignetting & CA very decent
3) IQ stopped down by 1 stop and more - awesome in every regard
4) bokeh wide open - great smooth, creamy at foreground, background and transition zones
5) bokeh stopped down - no ugly bokeh / circular aperture blades please!
6) AF - accurate, fast (full USM/HSM preferred, will consider STM if well implemented)
(ie 'extra bonus' points) criteria:
7. build quality - solid, metal mount, usable focus ring with FTM focus
8. weight / size: not too heavy / big (less than 500gr is possible)
9. IS - image stabilisation of 4 stops would be sweet (if not to the detriment of the above points)
10. filter size of filters that I have several of (ie 58mm, 67mm or 72mm preferable).
11. close MFD (so I can get nearby items in focus - for that 'effect')
12. price less than $800 if it ticks the above boxes (even if initial RRP is a bit higher, I'm interested in the online / street price after some time).
Now, if Sigma produce a great prime, and there are 95% of people / reviewers happy with it - no QC / AF issues - then I'll happily buy Sigma. I currently already have 1 Sigma lens (UWA) which I'm very happy with.
So... the same is on: Canon, Sigma (& others?) Who's gonna produce such a lens (first)?