The problem is in funding and time. You know that aircraft designs are not as simple as designing cars or other machines. Because of the risks involved it needs to be tested extensively and costs money.
So there are 3 aspects to it:
A) finding a bigger engine and establishing overhauling facilities for it. Iam assuming it is going to be Russian as well probably AL series. WS10 is too unreliable to be considered at the moment.
B) Redesigning the whole fuselage with associated testing and evaluation(therefore time and money).
C) the likelihood is the design characteristics might not alter tremendously and therefore there is too much of a nelement of predictability. You will laso not bring any newer technology as the source remains the same.
So you have found a very expensive way of producing a J10 equivalent of JFT which you were trying to avoid, it will come in 2020-23 assuming you start tomorrow, you cant do it alone which is why it wont happen as the Chinese will not allow you to produce a plane which will compromise sales of their J10 series.
So all in all not a good idea.I think wait for a couple of years to get a better RD series engine for JFT, increase the composite element of ti to reduce the weigh and add a couple of hardpoints for PODs and new ewsuite and Radar and you have what you need on a more ceconomical manner.
Hope this helps
A