One of the main problems with TCAS is that it is designed for the civil sector, for aircraft in benign flight regimes that maintain profiles designed to keep them away from each other. Trust me, if you have 3 aircraft 1000ft separated in the same CAS stack you will get so many nuisance warnings from the TCAS that it will be turned off, or worse ignored in a jet which is constantly giving you other audio warnings 90% of which are nugatory.
This was predicted and realised with ECAS which is turned off before take off as it generates so many nuisance warnings. TCAS is really only useful in a FJ in the transit (when you are behaving like an airliner) or for finding the tanker on a dark night.
Again, TCAS is great and IMHO should be fitted to all military aircraft but it would not have prevented the vast majority of FJ vs FJ close a-boards in the last few years, because it would have been turned off (the exception to this is the Moray Firth Tornado crash where it almost certainly would have saved lives, hence I still think it should be fitted and used where appropriate)