Battlefield 5's battle royale mode, Firestorm, probably failed to meet the expectations of DICE and EA. This isn't necessarily indicative of the mode itself; Firestorm was definitely a solid Battle Royale, though it wasn't without its problems. For the most part, Battlefield 5 released in a fairly lackluster state, and Firestorm wasn't there at release. By the time Firestorm actually came out, the hype for Battlefield 5 had died down, and so there wasn't much excitement for the new battle royale mode.
As mentioned above, while Firestorm was a good time, it definitely had some things that could be changed and improved upon for a future Battlefield Battle Royale, if one is on the way. If Battlefield 6 has a battle royale, here are the things that it should change from Firestorm.
The Battle Royale Loot Pinata
This isn't a problem unique to Firestorm: Warzone has this issue, too. Upon release, when characters in Firestorm died, all of their loot, every single tiny, insignificant bit of it, dropped directly down onto the ground. This made actually looting enemies that players killed a task tedious enough that it should have come with hourly pay. In order to loot a specific thing a player wanted, they would have to look just a couple of pixels up; but look one pixel too far, and they had to line it up all over again. The situation was improved somewhat after release, but Battlefield 6's rumored battle royale needs to release with a better looting system than Firestorm did.
There are a couple of solutions to this. The best solution is to handle loot the way Apex Legends and PlayerUnkown's Battlegrounds do. When players die, they drop a box, and players can sift through that box and easily see what they want. While this isn't the most inherently fastest ways to determine what loot a player has, it does mean grabbing exactly what a player wants very simple. The other solution would be to greatly increase the range at which an enemy's loot disperses when they die. Make loot have to be a certain distance from the next nearest loot, and everything would be spaced out enough that it's easy to see and grab exactly what players want.
Weapon Attachments
Part of the fun of Battlefield is customizing the weapons. While it's understandable that this wasn't a feature in the WW2 shooter of Battlefield 5, if Battlefield 6 is indeed a modern shooter, it should treat weapons and weapon attachments like PUBG does as opposed to how Firestorm and Warzone does. Let players pick up an attachment-less weapon, and then find the weapon attachments that they want on the ground and equip them.
If Battlefield 6 is set in the modern day, then there should be tons of meaningfully different attachments available in the game. Letting players pick and choose what attachments they want to loot gives them a bit more agency and ownership over their weapon in-game.
Multiple Battle Royale Maps
This is another problem that was largely due to the setting. The map in Firestorm wasn't bad, it just wasn't too terribly interesting. The setting limited what aspects could be present in the map, and considering there was only one map included in Firestorm, it meant that the map became a little uninteresting to spend time on after a few days.
One of the best solutions to this problem would be to just have more than one map, in the same vein as PUBG or Apex. This could create similar problems to PUBG, where there are certain maps (Miramar) that most of the playerbase doesn't like to play on. But, it would create a variety of settings, meaning the mode wouldn't have to hit a ton of different notes in the same map, like other battle royale games attempt to do.
While creating a great Battle Royale map is an absurd amount of work, DICE is already well-adjusted to making huge maps. The maps that fill the normal multiplayer modes in Battlefield are already huge. While not necessarily as big as a battle royale map would need to be, DICE clearly has the chops to make quite a few big maps. These maps could be on a rotation like Apex does with its own, or players could just be put on a random map, like what happens in PUBG. Either way, this would mean there could be a very wide variety in the settings, and it could keep the mode fresh for a longer time.
Battlefield 6 is in development for PS5 and Xbox Series X.