I think it would be, it could help a lot of people who didnt bother with the first few games catch up. I never got into Gears of War 1 when it was out but I was playing Gears of War 3 the other and kind of regretted not playing the others first, I dont get any of the references to the older characters, people who have died etc and this could help me stay on track of the storyline without having to play them myself.
Other than my own reasons it seems very ambitious but a challenge worth doing, if you are doing all three would it not be better to do walkthroughs of each one showing how to get past this part and that part? Of course its entirely up to you and its still a good idea.