That's the beauty with sodium ion batteries, they are generally considered to be even less flammable than already pretty safe LiFePO4.

Unfortunately that's not exactly true.

Aqueous sodium ion chemistries like Na-VPF and Na-tmCN are more fire-safe than lithium, but they're also not as developed/available yet.

Na-NMF, which is what a random off-the-shelf sodium cell is likely to be, is actually more flammable than LiFePO4.