This is essentially a variation of a previous feature request. If the cords for each song were written/stored in the key actually played, with an optional per-user configurable transpose-offset that is applied on the fly this would be a lot more flexible, and consistent between musicians in a band. The per-user offset, when used, should ideally also be adjusted whenever the stored chords are saved after transposing although it is is impossible to fully automate all changes regardless of instruments used and personal preferences. Valid input for the offset would be -11 to +11 semitones or NULL (not used). 0 (zero) would mean that the offset is used in case the song later is transposed. (for example up one or more semitones for an acoustic guitar player).
For example a song in Bm played on bass, keys, guitar and mandolin would be stored in Bm. The guitar-player may use an offset of -2 to play with capo as if it was a song in Am, while the mandolin player may prefer -4 (Gm) with capo at the 4th fret. A beginner on keys may prefer to play in Am (-2) transposing 2 semitones up on the keyboard, while the bass plays the chords as written (no offset).