[Note: This could either be a scenario or part of the config for certain games.]
This scenario is referring to an addition that would allow blazes to spawn naturally in the Nether by taking up the spawns of a signficant amount of zombified pigmen. These blazes would have the option of dropping both blaze rods and nether warts.
This addition would help to counter the amount of time spent in the Nether trying to get potions as well as would ensure that potions are possible to obtain regardless of if there is a fortress within the relatively short 1500 x 1500 border which shrinks significantly by the time players are able to access the Nether dimension.
[If applicable, wither skeletons could also spawn naturally in the Nether.]