In response to the apology that the 500x is not intended for 500 owners, and therefore the amount extra processing power is irrelevant:
The 500 was sold with (at least) half the processing power that it requires. For this reason alone, the DSP limit is and has always been a design failure, allowed for the sake of lowering the price-point. As someone who's been using one from the start, I fully understand that it is what it is - But I will not make excuses for Line 6. Merely having grown accustomed to the unit's shortcomings does not mean that I have forgiven them.
Let's be completely honest, here: The X3 didn't overrun its processing power, because what it had was sufficient for the requirements of its firmware. The 500 is the successor, but didn't adhere to the same standards of performance - The hardware simply didn't meet the requirements demanded by the new modeling algorithms. After enough time passed in the 500's lifecycle, the computing hardware market allowed for increase in processing power for the HD500, while keeping it at the same price point. And that's what it all comes down to:
Each succession of floorboard POD has to be kept within a certain price-range. And for the last two iterations, corners have been cut to keep it there. Obviously, no one is going to admit that anyone, at any point, was short-changed.
The demands of firmware, software, etc. require a certain level of processing power, in order to function as intended. The HD500 product was approved and sold without those requirements having been fulfilled. Even if the price is right, no one is obligated to ignore the fact that it is an engineering failure. We know that it's an engineering failure, because Line 6 has never officially said that they specifically designed it to suck.
Or did they? Here's how marketing spun it in the manual: "We’ve offered up a whole lot of sound possibilities in POD HD500, and it can take some serious Digital Signal Processing (DSP) to run these goodies. Rather than limit your creative potential with fewer Models or signal routing options, we chose to implement a “Dynamic DSP” system, which dynamically assigns DSP resources to accommodate your tone configurations"
That sounds better than "Even with workarounds, it doesn't work like it's supposed to. Five-Hundred Dollars." That's essentially been the case, twice.
Again, I endorse the HD500 for my amp-modeling needs - To the point that I would have bought a 500x that finally fulfilled the hardware requirements. But it doesn't. I understand why that's the case, but still think it's lousy. That's merely my opinion, informed by facts.