There’s some discussion here regarding an iPhone app, which also includes calls for a simple control app. If that eventuates it may provide a role for older iOS devices, but nothing is confirmed.
As the owner of two stranded iOS devices I feel the pain. But it’s not the first time I’ve experienced backwards compatibility or minimum hardware requirements and the march of progress dictates it’s not likely to be the last.
I can see how a “transport” style control app might be useful. Starting a playlist in Roon for a dinner party from a touchscreen say, but wanting to control Volume or skip tracks from the table.