If you are really that concerned about the limitations of the 10 Hole diatonic harmonica, then the solution is to play a chromatic harmonica. A twelve hole chromatic gives you all twelve notes of the chromatic scale over three octaves. Enough for most folk I would say.

Of course the chromatic harmonica has its own set of limitations. It is essentially a melody instrument with very limited chordal possibilities.

Personally I like the simplicity of the 10 hole diatonic harmonica and if there are key changes, then it is not too difficult to hold two harmonicas in one hand and swap from one to the other. The harmonic possibilities are also attractive. The Richter tuning was designed to enable the standard tonic dominant harmonies of many popular tunes and it works well for many folk tunes. The Paddy Richter variant extends the possibilities, especially for folk tunes in G which often go down to a low D and need the E below G.

10 hole diatonics are also cheap enough to be able to buy them in a range of keys.