IR guided fire and forget is fine, but undoubtedly quite a bit costlier than the basic laser-guided one. If you want to use it against jet engined Shaheds while launching from the ground, you definitely need larger rocket motor, i.e. costlier interceptors. But that might be fine, the jet engined Shaheds are not as cheap as the basic ones anyway.

Actually, I am surprised they still use the Shahed platform for the jet engined drones. A Reaper-like platform with high aspect ratio wings would be much more aerodynamically efficient, allowing longer range/loiter time/larger payload. It is definitely more expensive airframe, but that jet engine might be the main cost factor anyway.

Re: IR seeker against plain Shaheds: does the basic weedwhacker Shahed have enough IR signature? (More precisely: does it have it if you did some basic precautions - cover the engine, some mixing of the ambient air with the exhaust.) The power level of that engine (= the whole source of IR energy) is quite low...