In this case, it will actually just work. People have been using USB audio DAC's since at least 2002. Unless you're using something aimed at professional musicians with a lot of inputs and outputs, it's just plug and play with class compliant drivers. Linux, MacOS, Windows, Android, and iOS all just work.

Obviously, until Apple switches to USB C, we will have separate USB C and lightning cables. That's inconvenient.

The argument for removal is that it's redundant. The USB or lightning port can transmit audio, so remove the 3.5mm and suddenly you have more space inside the phone to put stuff and it's probably slightly cheaper/easier to water proof.

edit: I feel compelled to mention that 3.5mm has issues as well. Cheap 3.5mm cables are often slightly too large or slightly too small which cause contact issues and wear on the port over time. Dirt/fuzz get pushed down into the port sometimes. Scratches or dirt can make the connection bad and cause noise when moving the plug. For a while we didn't have a standard TRRS configuration but I think we figured that one out now, for the most part. You can actually buy a 3.5mm TS cable which is missing a channel on the normal TRS or TRRS and therefore will not work, while looking almost identical to the correct cable.