Saw this thread last weekend but did not have the time to respond and then forgot about it until today. As always, I am not trying to offend anyone but think it is vital that parents/players have basic information that will provide a starting point for additional individual research.
In my opinion, coaching stride length is like treating medical condition symptoms yet never doing anything about the condition itself. Appropriate stride length should be byproduct of effectively loading the back hip/posterior chain and using that to create momentum down slope of mound. In order to effectively load back hip, the pitcher must have appropriate mobility, stability, and strength.
When coaches focus on the symptoms, they often screw up the natural timing that is associated with throwing a baseball with intent and command! I just received a vid last week from one of our players who played summer/fall ball with largest travel ball club organization in our state. They sell parents on all of the ex-pro's working for their organization. When this player left us at end of spring, he was in a good place and had progressed enough that he had moved from JV to V and was getting innings during varsity games. The vid I received from him last week included a message that said something like; "Coach can you take a look at my video and see if you see anything I can fix because I am losing velo?" After looking at the video, I was fired up. A number of things had changed. I asked if he had been coached to do anything differently and he said that his 25-year old ex-pro coach was working with him on changing his arm path.
I know the initial post was in regards to stride length but it goes back to my point regarding symptoms. Because he was so focused on making the arm path change, he was no longer throwing with intent which effected a number of other things including his stride length (now shorter). The last thing I am going to do is work on the symptoms. My first recommendation was to see our local PT and get an assessment. We will then address any mobility, stability, strength issues while we get back to throwing with intent. I am betting that this will get him moving in the right direction again with improved velo and command, without ever mentioning stride length.
Just my 2 cents.