I expect opposition from the usual suspects over adding another buff to top end gear, but this should be counterable by pointing ought the likely overall decrease in auto-farming -fishing that would resulrt from less replacement gear bing needed.
I have some hesitancy over this as it insulates players against the costs of poor play (the general reason one ends up in lava), but the upcoming ability to remove specific enchantments via datapacks largely obviates this concern (at least for SMP groups who want a more 'hardcore' experience).
Something not clear from the description is what happens to the gear bearing the enchantment when it falls into lava…
Even if the player dies, I would prefer this enchantment not to cause the protected gear to respawn with the player.
It would seem preferable that the gear simply float on the lava (per 1.13+ item in fluid mechanics) [Having the item sink in lava (which is far denser than water) seems illogical, but would present a greater chanllenge to retrieval…]
In either case, the item should be subject to the normal five minute despawn rule if the chunk is loaded.
A further limit on the enchantment power (should one become desirable) could be to make it single use: an item being immersed in lava would survive (subject to the item despawn rules), but with its fire resistance removed.
A minor point, but – as there is already a player effecting status effect of this name – renaming the item effecting enchantment might help prevent confusion.
Rollback Post to RevisionRollBack
WARNING: I have an extemely "grindy" playstyle; YMMV — if this doesn't seem fun to you, mine what you can from it & bin the rest.