If you use Metal or similar you'll have to either show users of other platforms to the door or to support N such APIs. Most would prefer to reduce that number not multiply it.
All that cheering for Metal is not sincere. Talk to actual developers who are forced to support many APIs because no one cared to make one cross platform work well. The bottom line, we need less of lock-in APIs promoted as the way to develop games.
In some cases. In other cases engine developers support multiple back ends and for actual game developers this is simplified by using that engine. But in any case if the game wants to be inclusive rather than exclusive the burden of supporting multiple APIs will show up. Either for studio developers themselves or as expense to hire contractors who do the porting or this will fall to engine developers.
All that cheering for Metal is not sincere. Talk to actual developers who are forced to support many APIs because no one cared to make one cross platform work well. The bottom line, we need less of lock-in APIs promoted as the way to develop games.