I think the general thrust there is to deal with the present opportunity, i.e. a limited population from a know source where precise identification is likely to be successful. It could also be a good test to determine the procedures that would be required when identifying future remains.
Your main thread there is not about the science of DNA testing, its practicalities or its costs. It is about sending letters to MPs about these limited number of remains. You put this thread here which is presumably to widen the debate.
My point is that if the law made DNA testing obligatory on the authorities, then a DNA bank would be built up. The cost and effort for a limited number is not really "cost effective". The cost of a letter to an MP (them answering it, getting replies from Gov Ministers, etc) is roughly the same as 1 DNA test. For 50 letters you could get the whole testing done.
These remains are not a "special case", but get attention because there is a group. In the same way that a coach crash with 50 fatalities gets more attention than a car crash with one death. The one skeleton dug up next week is, to me, just as important to identify as the group.
But the way of dealing with it, needs to be a system. Set up a DNA bank, and set up a DNA testing procedure for people who could prove they had dead relatives in France in WW1.
There are all sorts of other practical problems - the bones are in France, therefore outside the jurisdiction of UK law (I assume). So you have to get co-operation of French Government. You need to agree what markers are tested - the more DNA markers tested the more expensive each test. If you limit the markers to, for example male markers, it would be a lot cheaper, but more difficult to track the male line to living males.
So do you have the figures for a DNA test on a set of bones, and the cost of the different DNA tests on living people to make matches. You need those costs if you are to get anything done. In the end, I am afraid, it will come down to "funding". And if you limit your campaign to just this group, then he decision making process of politicians is so long that the bones will be re-interred before anyone agrees. They will just kick this into the long grass.
Then next big find of unknown bones, same letter writing will occur.
I am not knocking your efforts here, they are commendable. But I honestly believe there is much more to this than this one group.