A Biden Admin official is saying Pfizer is expected to apply for third dose boosters for all adults in the coming weeks. I think this will eventually be the case, just a matter of when.
The FDA was fairly onboard with broad boosters and so was Walensky, so I think when they do apply it will get approved.
At the prior ACIP booster meeting there was some resistance to boosters for everyone. Though effectively ~70% of adults are currently eligible or will be when they hit the 6 month mark under the guidance that Walensky adopted. And right now eligibility is by self-attestation, so an ineligible adult who wants a booster wouldn't run into any verification.
As for the data, the third dose is bringing vaccine effectiveness up to pre-Delta levels, and also raising protection against infection. We aren't seeing much need for boosters yet in young, healthy adults, but we'll probably start to see waning immunity for this group in the coming months.