In what ways do you think Beta could be playable?
In my mind some ideas could be that during a time where Aloy would be absent from The Base there would be an opportunity to enter into ZD facility that would only be available for a limited time and given that they both have Alpha Clearance Beta would need to come to open the door, most likely with several others with her for protection only for them to be separated and Beta would need to progress through herself using her own skills and intelligence rather than combat powers
Regarding Elisabet, maybe she could be playable during a prologue or similar Interlude chapters showing her own in real time and not in holographic displays about the events of Op Enduring Victory and the building of ZD or maybe it could be set earlier in her life and maybe setting up something with a key point of the game like Vast Sliver, maybe linking to the events of where she and Tilda meet at an AI Event with it being in relation to Vast Sliver as a timeline of when was not given, with the possibility that choices made during the mission from breaching dialog options could impact the outcome of the story