QUOTE(Mote @ Wed 20 May 2009 0757)

Helmet mounted display is doable, but DAS and EOTS won't fit as I understand it. Cameras are too big.
The F-22 PO is apparently looking at adding DAS functionality to the AAR-56s. I think the principal problem with the idea of back fitting the AAQ-37 cameras is the “aperture canoe” behind the nose gear door on the F-22 is too small to accommodate the bigger cameras. What I found interesting is despite the video’s claims, LM officials have commented fairly recently that they don’t think DAS is much of a tactical advantage in a WVR fight.
EOTS is a whole different animal and would require the addition of a chin aperture like the F-35 has. I think this would be more of a fiscal than a technical hurdle as a lot of work was done for the AIRST early in the F-22 program which has a very similar aperture in the same location. IIRC they even went as far as pole testing the final configuration before dropping the AIRST entirely.
QUOTE
Given that the F-22s have already gone on upgrades costing a hundred million per plane apparently I doubt it could be done for "not too much."
Not that much. The combined cost of the next two upgrades -- increment 3.1 and 3.2 -- is $8.3 billion. Most of that is R&D and as I recall the actual cost to upgrade each jet is around $10 million. What’s interesting is that the current upgrade path for the jet is heavily biased towards A-G. Here are the latest known upgrade spirals (as of Jun ’08):
Block 30 Increment 3.1: SAR modes (APG-77v1), self targeting for JDAM, SDB capability (Global Strike initial Enhanced)
Block 35 Increment 3.2: MALD, Enhanced SDB capability, multi-ship geo-location, AGCAS, AIM-9X, AIM-120D. (Global Strike Enhanced)
Block 35: Increment 3.3: (Unfunded presently) Mode 5/S transponder, additional automatic radar modes, GMTI
There’s some conflicting information on whether the SDB capability is in 3.1 or 3.2. Even more interesting is the still undefined increment 4 and 5 spirals which changes the type designation from F-22A to F-22C. Increment 4/5 will add the following:
Full spectrum Airborne Electronic Attack
Full spectrum C2 Battlespace awareness
Full spectrum Network-Centric warfare
Extended LO-Combat range
Advanced Weapons/Moving Target Attack