For those of you who don't know, this will most probably be the only Poirot story by Agatha Christie NOT to be included in David Suchet's definitive portrayal. If you haven't read it, here's a link to a blog with the entire text: http://katanageldar.wordpress.com/tag/the-lemesurier-inheritance/.
I think there are several reasons why we most likely won't see this story on screen:
1) Its length. Since 2004, all Poirot episodes have been approx. 90 mins long. To adapt this story, it would have to be expanded into a 90 minute TV film, which, to be honest, I don't see as an attractive option. The story itself is very conventional and almost a Sherlock Holmes and Doctor Watson look-a-like, and I don't see it working as an expanded film. Having said that, possibly the only ITV Marple episode I have truly enjoyed was a short story, 'The Blue Geranium', expanded and adapted as a 90 min film. In other words, this point is probably not the most valid one.
2) Its setting. I know the Poirot producers have become experts at relocating Christie's stories in chronology terms (see my other blog for more on this). However, this particular story is supposed to be the very first case Poirot takes on after Styles, i.e. immediately after WW1. One of the main characters is a friend of Hastings from the army. No disrespect to Suchet and Fraser, but they both look older now than they did 20 years ago. So I very much doubt they would manage to make them look close to 30 years younger... But again, settings could be changed and story lines could be bent a little to make this work as a 1930s adaptation.
3) ITV Marple. This may sound silly, but the adaptations of Poirot and Marple for ITV are clearly interlinked. They have the same producers and much of the same crew, which means whenever the crew isn't working on a Poirot episode, they are frequently working on a Marple, as ITV tends to commission the two series together. What has become the norm for the last couple of years is that ITV commissions 4 Marples and 4 Poirots, a total of 8 films, to be made at the same time, by the same production company. This time, ITV has commissioned 5 Poirots and 3 Marples. I think it is likely that ITV wants a certain number of adaptations from each sleuth in each series, so they didn't want to push their luck and go for 6 Poirots and 2 Marples. But this is pure speculation, and I have nothing to support my claim.
3) Money. Sadly, this is probably the most likely explanation. The final series of Poirot nearly didn't happen, because of these financial issues. ITV seemed unable to find the money to carry on making the episodes. Somehow, they changed their mind, probably because of the success of Downton Abbey, but they have probably still gone for as few expenses as possible. Meaning that if anything can be cut without it being too obvious, they would do it. I think this is the case with 'The Lemesurier Inheritance'. It was an easy way to save money and thereby make the remaining adaptations better. But again, I have no proof of this being the case.
But in all of this misery (even if it is slight misery, considering that we actually get almost all the Poirot stories filmed!), there is a light at the end of the tunnel. Possibly two lights even. Firstly, David Suchet was asked on Twitter a while back whether The Lemesurier Inheritance would be referenced in some way in the final series to make it complete. His answer was "I hope so." (see below).
Secondly, David Suchet keeps referring to the fact that he will have starred in every single Poirot episode ever written. A typical example of this was in an interview with BBC's Andrew Marr. In this interview, he even corrected Marr, stating that there was one "story" he would not be starring in, i.e. Black Coffee, before he explained that he would do that at Chichester (see previous post). Notice that he had every opportunity to explain that there was also a short story he wouldn't be doing. Of course, that's probably because he doesn't want to remind people that there is a story they have had to skip, but it could, again, mean that they have something planned for this story in the five remaining adaptions. Let's hope so and keep our fingers crossed! (As I have said before, though, this short story is a minor loss and we can easily live with the fact that it won't be done if that is indeed the case).
UPDATE: According to an article in Radio Times (2012), 'The Lemesurier Inheritance' will be incorporated into the adaptation of The Labours of Hercules! (See the link: http://www.radiotimes.com/news/2012-10-07/david-suchet--there-will-be-no-more-poirots--the-moustache-is-hung-up). I have no idea how they will make that work, but in any case - it means that Suchet's portrayal will be complete (in theory).
Also, I think it's important to point out that Suchet actually narrated the audiobook version of this short story! Consequently, he has "performed" in an adaptation of sorts of all Christie's Poirot stories - regardless of how the short story will be referenced in the television series.