6 month update:
Luke, how did you know? I *did* end up making another pack entirely (a canyoneering pack, a bit heavy for BPL) and then I took the Chili Pepper apart, made a lot of changes and put it back together. I've learned a lot since I first posted this backpack, so it was time to improve things (I've since started my own business sewing bikepacking gear and you learn fast when you sew every day!).
Overall I was happy with the pack before, but when you open up a pack and have the opportunity to change things after this much time . . . ooh boy. I meant to change like 2 things and ended up changing about 10. Lots of little incremental changes and also a lot of reinforcement of wear areas. Shows how much I've learned. Enjoy the ride.
The first thing I did was make the pack smaller, by making the side panels smaller. So it's just as wide, but less deep. This was key for making the whole thing a reasonable project and not super frustrating - there was very little seam ripping involved! I just cut next to the seam and only had to replace the front panel (making the side panels smaller made it a bit wider). You can see that I also replaced the side compression straps by making two of them, which both tighten in the middle of the pack - in my prior system the roll top would "eat" the ladderlock buckle at the top.
Another thing I did, that you can see in both that picture and the next one, is to make the bottom panel curve upward. This is surprisingly easy to do, as long as you want the upward curve to match the side panel curve - you just lay the bottom and side panels on top of each other and sew a curve into them; turn it inside out and you have this nice 45-degree curve going on. I have a good picture of sewing this somewhere if anyone wants to see it.
Both of these changes have made it pull back on my shoulders a little less.
Also you can see there that I replaced my lycra mesh (which already had gotten some holes in it) with leno lock mesh. I needed some pleats and probably could've made it a little bit bigger (it was a 12" piece of leno lock on an 8" panel of Xpac). But it'll be enough to get a wet groundcloth and tent in there, and of course there's dirty sock storage at the bottom. So that's good enough for me. It also makes a great pocket for storing fish (in their own ziplock of course).
Another big change was the hipbelt attachment you see above. The buckles I was using before had too much slippage and always felt a little clumsy to me. And since I've been sewing so much bikepacking gear I've become a believer in the power of velcro - it really is pretty strong stuff given sufficient surface area. So I sewed on D-rings and made the hipbelt attach with 4x2 inches of velcro on each side. I've been super happy with this arrangement so far. I've also been running the hipbelt behind the folded sleeping pad and I've been happy with that.
Here's the last of my intended changes, and the original impetus to take the pack apart. One of my poles cut through the bottom of the sleeve! That's through 1 layer of 1000d cordura and 1 layer of Xpac. And in retrospect I was pretty stupid about things - Quest sells a dome-style cap that's perfect for turning the sharp end of the pole into something nice and rounded. So I bought a couple of those and glued them into the bottom of the poles with contact cement. Then I ripped out the ends of the sleeves and reinforced them both with more cordura.
Now onto the minor details that I worked on. I replaced my shoulder strap ladderlocks with side release buckles, because it's a great place to stow a hat while hiking. I also beefed up the attachment (which was pretty weak). I didn't want to take my shoulder straps apart, so I was more limited in what I can do, but double bartacks should be plenty strong into those materials.
I also beefed up my daisy chain . . .I can't believe I sewed it so weak (you can see the original stitching there). Nowadays I always do tight zig-zag stitches that go over the edges of the webbing a bit (someone here taught me that). I didn't feel like taking the shoulder straps apart, and I don't use the whole daisy chain, so I just reinforced the spots that needed it with my speedy stitcher.
My final change to the shoulder straps was to change the load lifter buckles to camming side releases. Sure, these are heavier than a ladderlock, but I *hate* slipping loaf lifters. Every pack I've ever had I've had to readjust the load lifters while hiking, and these are the only buckles I know that I won't need to do that. The cam buckles I had on before didn't cut it. If someone made just the ladderlock+cam part of these I would use that, but this works. Maybe my next pack will just have shoulder straps attach higher up and I won't use load lifters at all.
Another important change was to get rid of the cam buckles that attached the frame to the pack, and replace it with velcro that double-backs on itself (using the same looplock that the shoulder straps attach to). This is a design I copied from my canyoneering pack, which just has two curved stays (not connecting at the top) with velcro going over the tops of them to secure them down. I've carried some pretty hefty loads with the canyoneering pack and had no trouble with that system, and it's lighter and cleaner than buckles.
This is the last change, I promise! I also beefed up the haul loop; my old one with grosgrain felt a bit flimsy. Not an important thing for most hiking, but some of my Grand Canyon trips involve hauling packs up steep bits and I'd hate to watch my pack fall off a cliff!
Since making all of these changes I've taken it on one trip, packrafting in the Bob Marshall. That only involved about 20 miles of hiking, so time will tell, but I'm super happy with it so far.