Guys, I don't actually think the J-20 is going to enter service any time soon... I think that it serves more as some technology demonstrator in the same manner as the SU-47 did for the PAK-FA. The reason why I think this, is the fact that I find the design and size of the J-20 are way too impractical for a fighter-bomber during a possible dogfight.
The J-31 on the other hand looks (design wise) much more practical. Yes it looks like an F-22 but then again, nobody is going to win a fashion prize when designing stealth fighters because the design restrictions push all current stealth designs and even those which are still in development into a similar looking model. Just compare all the cockpits alone of the different fighters (even those which are still on paper) together and you will see that
ALL OF THEM look pretty much the same!
And this is why I also think that the PLAAF will probably work more towards the J-31 as China's principal 5th-gen stealth fighter. Just because of the fact that the Shenyang designers decided to play it 'safe' and base their designs on existing models instead of drawing out a completely new concept which might risk becoming impractical as well.
No offense towards the CAIC crew though, they were already able of rolling out an otherwise capable stealth jet that was able to fly and pull manoeuvrers and that is an accomplishment on itself alone!