After I did the CF, I decided I would just tell people to google the best sneakers that marathon runners use and then go try them on and decide. And buy 1/2 to a full size larger to account for your feet getting "longer". I used a low cut, trail runner from Merrell and it worked but I didn't need the waterproof feature or the aggressive tread. A running shoe for marathons has the support. light weight, and longevity designed in so it works on a camino. My shoes had holes when I was finished at the crease where the toe box folds over and over while walking. Although, all shoes take a beating, Merrell footwear is no longer my go to choice anymore.
I can understand your reasoning in suggesting shoes that are favored by marathon runners. I like the focus on recommending shoes which require less energy when you are constantly lifting legs when walking. Less weight means more energy available.
Perhaps I can share why I would recommend other styles of running shoes, and tend to avoid shoes marketed for marathoners. But if you are looking at the amount of wording below, I would not hold it against you if you decided walking the dog was a better use of the time that it would take to read this post..
The design focus of marathon-specific shoes is for a 'fast' and ultralight shoe. That is achieved by using less cushioning materials to cut weight, and limiting materials for motion control and support. Because marathoning is a short duration with no need to carry a backpack, as compared to walking with a backpack for long hours in a day, sacrificing cushioning and support levels to gain a lighter weight is a reasonable trade.. Runners can cover long distances, but they do so in a fraction of the time that backpackers, hikers, and walkers do.
I do recognize that there exists a wide diversity of people who have feet made of iron. They do not need or want a lot of support and cushioning from a shoe. These are feet that have highly developed structural strength which can deal with the stresses of long distance walking. Stresses that would make a large percentage of folks holler 'uncle' if shod in ultralight marathon runners.
I am among many others who have feet that either suffer from medical conditions, or that refuse conditioning and squawk at the thought of hiking and backpacking.
If I tried to force my feet to do long distance walking in a pair of superlight, thinly padded shoes, my feet would do a Mutiny on the Bounty. Right Foot would lead the rebellion and scream accusations of abuse and barbarism. They would then amputate themselves, set me adrift, and run away. They would view hiking in a marathon shoe as an unforgivable crossing of a line.
You are also on the right track about the idea of purchasing a larger size shoe, and that is an option to keep in mind when purchasing new hiking shoes or trail runners. It is important, however, to decide on exactly how much of a size increase is needed based on how a shoe fits. Specific size measurements are irrelevant. A shoe purchase needs to be assessed solely on how it fits-n-feels,. Once that has been achieved, then you will know what size needs to be purchased.
I do not need to know the label size of a shoe to know if a shoe is sized correctly. But, I could very well end up with an uncomfortable shoe that has a poor fit by relying on my stated shoe size printed on the box. Many an injured and blistered foot has occurred because a pilgrim bought a pair of hiking shoes based only their normal measured shoe size, and then adding an incremental size increase.
However, during proper fitting for hiking shoes, you may find a need to go up just a half-size to two whole sizes. You just won't know for sure unless the proper fitting procedure is followed.
A lot of folks share your thinking that when doing a long walk, the primary size increase to feet will be to the length. While that might occur, it is a small, fractional increase; the main increase to size comes from the width of the foot.
The reason so much emphasis is made on purchase a shoe with a longer length, is to have enough space at the front of the shoe to keep toes from banging into the shoe on downhills, and even with just walking over many hours..
A proper fitting assesses the width of the shoe, as well as the length. Again, proper fitting procedures will deliver the shoe size needed.