Very few drivers have been written, beyond handling low-level SoC stuff. The ones that have been are explicitly mentioned in the linked article, stuff like USB which leverages existing Linux code.

No keyboard, no trackpad, no GPU drivers (besides an unaccelerated framebuffer, setup and left by iBoot). There's some indication of Wi-Fi support, as it's a Broadcom FullMAC device (brcmfmac on Linux). But yeah, I'd say unusable without a USB hub and a myriad of external devices. Again, said as much in the article.