Taliyah W: How I think it should work
On quickcast: The cast should start as soon as you press W. With range clamping (I could get used to without, but I think it's much better with). Then move mouse in desired direction, and release W (like vector casting, BUT the starting of cast on first W press is important).
On normal cast: I don't know actually, I don't use normal cast.
======================= This way how fast you finish inputting direction is not that important -- Taliyah has high "strategic" learning curve (where to place your wall or E, etc), I don't see what adding "how fast you can mesh keys in the right order" adds to the champion, so would rather it not be a large factor if possible.
It took me a game or two to get used to original W. I really loved playing taliyah (> 100 games on her before last patch). But now.. played 4-5 games, still can not get W consistent, and with other changes (that deserve a post of its own), decided I'll abandon her, as she no longer fits my style -- learning to mash keys fast is not as interesting to me as learning to make right decisions. A pity, she was my favorite champion.