Interesting debate about the probes, but IMO we should worry ourselves more about other key capabilities first. Enough sets of DAS to start with, flight deck armour etc etc, all the role equipment we need to deploy the things would be nice.
IIRC, the common standard aircraft can be fitted with probes for refuelling. Assuming we have not paid extra to have the capability removed (such things have happened...), it should not be a huge faff to retro fit an AAR (receiver) capability. That of course depends upon availabiity of kit and then a trials programme that should only need to focus on the differences between the multi-national airworthiness regs and our own (as per the rest of the ac capabilities). There was no customer requirement for a refuelling capability, hence one has not been bought. If that subsequently changes (engine performance leading to reduced range, perchance?), then changing our minds should not be tricky, expensive, but not tricky.
When you buy to a budget, you can't have all the toys, you have to pick the most important ones. Roll on another couple of C-17s.