Complying with the Midi 1.0 standard is an obvious option. Old instruments are designed to handle 31,250 baud because that is the standard.

If a new device does not transmit at exactly that rate, it is sending a different protocol, not Midi 1.0 (and the Midi 2.0 requires implementations to be backward compatible).

transmission of midi frames

Midi 1.0 is based on bytes not frames. If you are sending frames, you are sending a different protocol, not Midi 1.0.