If we take what Mr Lothar says literally re completing it must surely be nonsense - I wonder what proportion of Pirate IM finishers meet his recommended mara times? Of course, it may lose something in translation - perhaps he meant compete rather than complete 
Re the 'take part and survive' culture, I am proud to be part of it (maras, ultras, cross-country ski maras...crap at all of them, made the cut-offs and lived to tell the tale!). Agree that some of us will never get that much faster with training, but are good at plodding on and keeping a positive attitude. High boredom threshold helps!
Still deliberating whether I could actually survive the cut offs for IM (4.30 mara pb!) but will probably try middle distance at least. Re 'the IM will always be there' - well, yes it will, but some of us are so middle-aged that there is a bit of 'now or never' mentality about getting round to it before the old bod gives out completely!
I wonder how Lother does his calculation. FB suggests 5x your Oly time...
In running I apply the Paula principle (take her time and double it to estimate mine). Spot on for my mara time. However, if I apply it to Chrissie Wellington's world record IM time that gives me 18 hours for IM which is not so encouraging...