I too, see the new stock as a sign they're looking more at design. But I don't expect them to redesign any time soon. First, they're building what they can as fast as they can, and can't keep them in stock.
A new design means shutting down a line for a while, and then ramping back up to iron out the kinks.
Also, there's the cost. HP doesn't really make any weapons themselves. Other plants build the pieces. All of them would have to be retooled. That means higher costs, and then possibly higher prices.
Lastly, they really don't have ANY competition in this space. While there are other cheap guns out there, they don't compare to HPs in reliability or quality. We all call the guns ugly, but we still buy them.
So if you ran a company, that was operating at full capacity and basically still had people waiting to find your guns, would you spend the money to create new tooling and then lose the production time to retool all of your lines and then ramp them up to get the kinks out? Especially since you wouldn't sell any more guns (since you're already selling everything you can make.)
I expect they might look at this if things slow down for them, or they get a new low end competitor.