I didn't follow the latest lenses anymore, but concerning corner to corner sharpness there aren't many f2.8 uwa's superb with a reasonable price.
Here below you find my order of preference (tested them myselves), pity enough not all f2.8 (only the first one would be the best but didn't test, out of my budget)
Canon 11-24 FL
Canon 17-40 f4L IS
Tokina 16-28 2.8 AT-X Pro
Canon 17-40 f4L
Canon 16-35 f2.8L II
As the 16-35 f2.8L II is too expensive with less corner sharpness than the others, it's time that a corner-corner sharp f2.8 is made next to the Tokina.
Is Sigma still not planning a sharp f2.8 Art or Tamron or another 3rd party brand (no Samyang, only with AF) ?
For marriages the 2.8 is advised like in churches, I will do a wedding with my 16-35 f4L IS.
F4 is double as dark as f2.8, I hope the IS will catch the problem not having 2.8