I had quite a good run, through Arena, and ended up both Supercharged and Berserking in The Wall, with an inventory full of rockets and medkits, so I figured I'll give it a try. Of course, after gloating over my freshly gained adv. rocket launcher modded to the teeth, to produce YASD two levels lover.
So, the Backpack was known to be implemented? In DOOM it allowed to carry more ammo, though it's been a looong time since I played that. :)
And yes, 9.8.7. seems somewhat more difficult than the last one. I seem to die at earlier levels, and character progression seems a tad slower. No evidence on that, though, just an impression.