The suicide scenario is highly unlikely, also technically very hard to grasp. But if nothing else fits so be it.
There is however another scenario, that somehow is not mentioned (yet?)
The pilot entered severe IMC conditions, descended to maintain, then get back, ground vision. He made a distress call (he did; that is NOT what you'd expect from a suicide mission..)
The area is very hilly. There are windmills and high tension lines on top of the hills. There are two rather large ones less than a mile from where the body was found. There is a high tension line with high towers north/south in close vicinity.
While flying low and fast he saw the windmill/high tension line, tried to pull up / push down / roll away but failed. The upper part of the cockpit was ripped off and the pilot thrown out. The damaged Piper stabilised and flew / glided for 3 more minutes down the valley then crashed.
Look at the pictures of the wreck. The left part of the cockpit is missing, the upper part is bent backwards with almost all parts missing. Remember the shoulder harness is mounted in the left upper roof of the cockpit, quite far behind. When it is ripped out it may very well at the very least unbuckle the others as well...
At first it seems to be highly unlikely. What are the odds? But then again, what are the odds of sending a distress call then push the door of a PA28 open against the wind and jump out in almost IMC .. Though unlikely, not much more so than the suicide scenario.
He may very well be just another victim of spatial disorientation - as has happened so many times before ...
Would like to know if they checked the windmills and high tension lines for marks ...