Best answer: Despite Battlefield Mobile currently being playtested in Indonesia and the Philippines with gameplay footage leaking online, there's no concrete news of controller support. However, Call of Duty Mobile does feature controller use, so it's fairly safe to deduct that Battlefield Mobile will follow suit to stay competitive with its nearest rival.
Why so sure?
With Call of Duty Mobile seeing massive success since its launch, it makes sense that EA would keep tabs on its direct competitor and implement some popular features into its game. Currently, COD Mobile supports the PS4 and Xbox One controllers and third-party offerings, though some functionality may be reduced. A popular option for both casual and hardcore shooter fans, controller support would likely be a consideration for EA, at the very least, the successful implementation on COD mobile being a clear reason for its inclusion.
There is other evidence, too, with Battlefield Mobile targeting the same demographic as COD Mobile and fans of the mainline series. With its trademark destructible environments and specialist class system, it seems that Battlefield Mobile won't deviate too much from its tried and tested formula. It would please long-time fans, many of them also hoping for controller support to help maintain interest in the game, especially if they aren't traditionally mobile gamers. EA is also implementing a free-to-play model, which can only help in a highly competitive and saturated space. Controller support would only aid them in keeping up with other games of this type that have already implemented this.
What makes controller support so important?
If you're used to playing Battlefield with a controller, the option to use one on Battlefield Mobile will likely be a desirable feature. Many long-time fans will be more comfortable using already familiar controller buttons than the touchscreen controls, and those that don't often play mobile games may not gel with them at all. Using a gamepad can provide greater control in a genre that demands a fast reaction time and precise movement. A mobile screen can hinder finger movement compared to a controller, and physical buttons are often less cumbersome and more reliable compared to their on-screen counterparts. Because of these reasons, as alluded to previously, some players may stick around longer if they can use a controller, primarily as other similar games have implemented this feature.
Battlefield Mobile needs controller support
While it is perhaps surprising that there is currently no news of controller support despite the game releasing next year, it looks pretty likely that it will be included as a feature. While it won't impact the overall quality of the game or its initial reception, it will surely be a highly requested feature if EA decides not to implement it at launch, especially as COD Mobile currently features official Playstation and Xbox controller support. With the mobile shooter market being full of top-rated titles, Battlefield Mobile will need to establish itself as a valid option, and controller support will go some way to ensuring that in the eyes of many gamers.