Something tells me that MKI numbers will further increase if MRCAs restricted at 126.
Don't believe it will. MRCA is very crucial and the IAF will exercise the follow on offer unless FGFA is simply too good comparatively.
MKI production has been delayed by a year, so the final lot of 42 aircraft will be delivered only by 2019, by HAL. It conflicts with Su-50 induction. The Russians have pending deliveries to Malaysia, Algeria, and Vietnam. Other than that they may receive orders from their own air force for the MKI and they have started production for Su-35 anyway.
Comparatively while MKI production ends and Su-50 starts, we can say the MRCA production will happen in parallel. So, we are adding one squadron of Su-50(may be more than one) and a squadron of MRCA every year. At the same time there is the LCA Mk2 production that will go on at a similar rate as MRCA. We will have 3 production lines for advanced aircraft by then, no point keeping a 4th open at the same time.
Starting Su-50 production would mean we are adding a superior aircraft instead of an inferior one as the MKI. So, capping MRCA numbers wouldn't mean increasing orders for MKI. Instead there may be an increase in orders for the Su-50. By then we may even know the progress of AMCA which will already be under flight tests. Why settle for less?