my TL/DR:
it can’t be done without an active “translator” device: monome’s hardware (FTDI driver chip) and apple’s software (no userspace access to USB-serial on iOS) represent incompatible design decisions.
the translator device has to host a usb-serial device on one end (for the grid) and act as a usb-midi device on the other end (for iOS).
if monome wanted to, future monome grid editions could possibly be MIDI devices instead of / in addition to serial devices. this would require substantial hardware changes and a total firmware rewrite, and would be of no use for any user of an existing grid.
it apple wanted to, they could support USBSerialDriverKit on iOS like they do on macOS. i’m not honestly sure why they don’t, but i’d guess its a combination of increased security liability and a total dearth of commercial applications.
no. i don’t have time for it and generally don’t care about iOS. it’s sort of a fun idea in general but not quite enough for me personally. the principle is quite simple and could be hacked with two devices (like “2host”) or a single device (a number of MCUs have multiple OTG ports and can be host+device simultaneously.)