Is it possible to use the late 2013 21.5 inch iMac as an external monitor?

If not, will bootcamp remedy the issue? I really like the display on my iMac and I don't want to pay for another monitor just so that I can play my PS4 plus I don't have the desk space for it.

If it's still a no, do you think it will ever be possible?

I don't want to buy a capture card either. But if you own one, what are your thoughts on it? I may build my own gaming PC in the future so I want to know how does that bode with a capture card like the extreme cap U3 connected to my iMac.