Not really. Let's say you were doing 8+2 before (times five) with 8TB drives, and switch to 8+3 with 40TB drives. You go from 400TB of raw space to 440TB of raw space, but you also go from 50 drive slots down to 11. Even if both drive models are the same cost per terabyte, the latter setup should have a lower total cost.

But I would also expect these drives to be cheaper per TB, at least by the time HAMR is 2-3 generations old.

I think if you're in the market for 32TB drives, you're already using 20TB ones instead of 8. With 8+2 at 20TB you pay for 200TB and get 160TB usable. With 7+3 at 32TB you pay for 320TB and have 224TB available. That's 160% of TB paid for and only 140% of TB usable. HMR will need to be a sizable 12.5% discount per terabyte just to break even there.

If you only do 5+3 to keep the same 160T available, it's 256TB or 128% paid for and the same 100% usable, so an even steeper 22% discount to break even.

If you're going from 20TB to 32TB then it barely affects your RAID reliability at all. You don't need to increase parity in that case.

And nobody that's price conscious would make a 5+3 RAID so I'm not very worried about such an extreme scenario.