*Bravely steps into arena*
10/10 for as long as you want. Or 11/10 for a short moment. Or since it's really about sending a message: 10/10 for a short time to replicate modernly.
Well I'm not listing chemicals... but just like there's mint and chili for hot and cold sensation and they don't typically leave lasting damage (blistering is a psychological response and will happen from strong capsaicin (I don't know if there's any chemical related damage though...)).
There's also chemicals for most other things. Including pain.
So you could just inflict pain without degrading anything other than mental health. Then again, not much of anything goes above the pain/fear combination of drowning. Apparently agony levels have been well researched and that one is in a tier of its own.
If you're inflicting pain they may not die. Then again they could suffer trauma reactions like shock and die. If you do drowning it doesn't last long and there's no spectacle. Which, let's face it, is probably what this form of torture was about.
If we're in an area that's unethical enough to do this and are trying to replicate modernly; we might as well go the full monty. Expose the nervous system, lacerate it and use stem cells to increase it's area. Stick them in a vat to help the stem cells, etc. grow. Have bacteria engineered to only eat nervous tissue. Apply to the ends and watch the body struggle to outgrow the amount being eaten. I'd imagine it would succeed while energy is high (so you're still feeding them) but eventually would fail and the pain would additionally slowly have paralysis added. Then you'd have spinal tissue and lower brain eaten. So Pain -> Pain + Paralysis -> Death. You could replace neural impulses and failing organs with substitutes to allow an extra slot of brain erosion before death. Up to you. The hollow human effect of not doing anything would probably be more unnerving to would-be offenders.