JTO,
No not a doom merchant and well aware of the upgrades that all aircraft get - I was involved in this for a fair chunk of my time in the RAF so know exactly what is involved. Tweaking an existing system is one thing but adding a new function is something altogether new and never that simple. That it is flying on a similar radar is no guarantee that it will work on Sentinel and I do not doubt that there are other systems with greater programatic risk attached, but there is always a danger with this sort of upgrade that things may get worse before they get better.
If it works as Raytheon promise/claim, then great, but I will remain sceptical that such a change can be termed as 'a simple software drop' for nothing more than the simple fact that it is not.