Well, that’s not true. Sure, connect it over PCIE and all bets are off, but connect it over USB and you should be fine. If you’re being super careful buy a Bluetooth 3G module.
With PCIE you even have the IOMMU which can prevent DMA.
Yeah, but apparently the PS4 was originally hacked through bugs in the IOMMU. I basically don't trust an IOMMU that I don't have the source to and that hasn't been formally verified (so all of them).
USB3.1 supports DMA, but at least you can disable it in the driver, if the driver exposes that functionality or you are using open drivers.