G W-H, you are of course correct and to clarify, the only means of providing an accurate EAT is for the en route controller to retrieve the info from aproach control (located in the same room) who have the Exact EAT information in front of their worksation. This would require a greatly increased workload for both parties and as the en route worksations do not have EAT information available (the ones at Swanwick do however) it is usually left to a 'best guess' scenario.
I am recalling the MATS reference that you make but do not have it in front of me so i cannot guarantee this is correct but i think that we may provide the pilot with a "delay not determined" should the holding be weather generated or "delay less than 20 minutes" if we genuinely believe that there is likely to be less than 5 times around the hold. This was the case for the shuttle scenario and in practice the controller will do their best to provide some pertinent info along the lines of "expect once or twice around" or "3 A/C ahead of you, suggest you reduce now to MCS".
Even hazier in my memory is the requirements of a pilot for fuelling, is it not along the lines of enough for 30 minutes holding plus divert fuel, plus another 30 mins hold at alternate? I might be out on that but like the MATS 1, there are many rules imposed on ATC as well as the pilot, some are adhered to stringently and some don't often get used on a day-to-day basis (did you know that we are supposed to provide a time check to A/C outside of controlled airspace when telling them to reamin clear, no one has ever done that in front of me?!!!).
I digress. We will always try and provide as accurate a picture to I/B A/C as is possible but when we don't have the exact info at our fingertips it is often difficult to get it right for every pilot that requests.
Hope that helps
RP45