The question is what's holding up the deal from being finalized? The overall message conveyed which is also why the Western media has grabbed on to it is believing Chinese domestic fighters aren't up to par and China desperately need this fighter. When this deal was first put out by Pinkov, it was 36 Su-35s. Now it's been reduced to 24. Why is that if China needs this fighter? What's holding up the deal if China is desperate? If it were all about the engines, that would be more believable, so why don't the Russians just sell the engines if they weren't worried about China getting them with Su-35? The whole point is Russia needs to get the Su-35 sold to a foreign buyer to get the ball rolling. On top of that they're probably going to sell China an export version that is lesser to get others scared into buying the better export version. Just like with the Su-30. And didn't China get a horrible price for Su-30s? Others will need a better Su-35 to beat China's. If this is the sticking point, you can see how China is dragging this along on a fighter they don't need in order to just get the engines.
what's holding so long is couple things. The first one is number of SU35. The second is
China wants SU35 to be modified to able to fire Chinese missiles and China wants to the modification done first before purchase while Russia wanted the purchase done first before modification. Latest I heard, Russia relented on the 2nd demand.