But do we know the weight that the wingtip can support?
Probably around 200-250kg if the weight of the ECM pods like Sorbitsya-S is anything to go by since they are heavier than most SRAAMs.
Could you fit a PL-15 there?. Maybe, but you'll need a longer rail and reinforcements to take into consideration not just the added weight of both missile and rail, but also the changes in bending moment caused by having a longer, thicker, heavier payload.
The amount of hardpoints the Flanker family have makes this unnecesary, though, and you are probably better off just adding dual-rails to the existing rated hardpoints than trying to redesign the wingtip rail.