Whatever will come of it, the FAA are looking closely to their process regarding the use of Lithium batteries.
In my opinion, we are looking at what amounts to a "waiver". Going against prior restrictions, the considerations seem rather "special case". While granting their use, the authority seem to be asking merely for a "be careful" in return.
Generally, in contravening traditional safeguards, the applicant is required to demonstrate an excess of proof, test, and mitigation.... In this situation, it seems the favorable view from FAA is careless, hence their open ended command to Boeing: "Prove the safety of this equipment...."
That may prove to be impossible, especially so when considering that the horses have bolted the corral.
Right wrong or indifferent, it will be tempting for FAA to prohibit Lithium. That may let Boeing off the hook with Yuasa, and cause Boeing to do what is clearly an expedient, but a political one, return to and refit with proven technology...