From what I have read they are not removing the SAR/ISAR modes - just degrading them for a "monkey" version that is useless for littoral/overland applications. Since the limitations are enforced flexibly through software the periscope search feature will be left alone and should work fine.
I don't know, it doesn't appear to have it, but perhaps you know more.
Degrading SAR precision to greater than 3 foot renders it irrelevant for overland targets without severely degrading it for maritime use (ships are much larger than AFV/trucks). Similarly they are removing the Ultra High Resolution (UHR) ISAR modes; presumably some ISAR capability will be retained for manual NCTR. With the full precision modes those radars can tell you which ship got hit where as well as what damaged was caused, all at standoff ranges. IN aircraft won't be capable of that kind of resolutions which is fine I guess.
The P-8I radar still has excellent resolution. What the UHR ISAR modes will provide is more detail about the target, which is very useful for a number of purposes.
US is ensuring through technological means that the P-8I remains a purely naval asset. i.e. No sudden appearance of the P-8I near Punjab border acting as a mini-JSTARS cuing PGMs. Which is fine so far as the IN is concerned. The other CNI "removals" are probably because of the Indian middle finger to CISMOA and again no great loss.
To do this, you would need to have very good ground clutter maps in order to distinguish targets from terrain features. It would also involve extensively modifying the scan strategy for ground clutter. Even if the P-8I had the resolution, getting the clutter maps made for this radar is a task, which I don't think are available for test or deployment yet even for the USAF. Otherwise we would have had some news from the US about the P-8S variant in testing.
My view is that the P-8I is not significantly shortchanged in its advertised role for the IN - LRMP/ASW.
Air to air mode is intriguing. Useful to have no doubt but I am having a hard time coming up with use cases where paying extra for it is worth it for an LRMP aircraft. Periodic air scan for self defense when in the suspected vicinity of enemy carrier based aviation? Search for UAV? ASW Helo?
Perhaps to provide surveillance over the seas to protect assets like "Bombay High" about 160 Km from the coast which provides 12-14% of India's oil.
I could see it being useful for providing AWACs type capability over the ocean and the Phalcon for use over land. We don't know Phalcon's capability in maritime conditions.
The cost is would be software development to optimize the scan strategy and clutter maps for A-to-A mode and extensive system integration testing. Its a one time cost that can be applied to the entire fleet that can also be applied to future aircraft. Once its developed for the IN, then its available to other Raytheon customers, but now the IN has a working relationship with Raytheon and IMHO that is also quite valuable.