Hi
I considered using 3.5mm connectors for serial midi in the beginning, but decided to use USB since it didn’t require external connectors and components, used I/Os or caused (minor) delays if using midi thru. It is possible to use one hardware serial port and one software serial port.
If you use usb to provide power, it’s a lot of extra wires. In theory you can also skip optical isolation and provide power over the fourth 3.5mm connector, but then you have to avoid connecting it to other TRS midi devices without a buffer.
Personally, I think it is better to use a MIDI bridge to connect it to other devices. (It is rather easy to build one using a microcontroller that supports USB host mode.)