There was the rumor not long ago that Canon has patented a new formula for a 35mm 1.4.
I want to buy a used 35mm 1.4, but I'm not sure if I should risk loss of value, in case a new one comes out shortly after.
Of course, there is also the Sigma option, but I'm scared of focusing problems which I have had before with Sigma. I also like the lighter weight of the Canon.
What do you think and what would you do?
...meanwhile you risking not taking the shots you want need.
It's not a collectible item (at least not yet), or a center display piece in your shelving, nor should be taken as an investment unless it's for work, or a very rare model; so get what you think you need, whithin your budget.
Prices will drop in time, no matter what - unless it's a rare lens. Lenses will depreciate slower than cameras, but don't let that stop you to get it now. There will be always something better lurking in the future, but live the present and get out enjoying your hobby.
Can't tell you much about the sigma - rent one or both and find out for yourself. As others said, the new model might be quite expensive to start, and guess what? - it will have a price drop sooner than later after you buying it...