Modal cadences are different from tonal cadences. For example, your idea of V - I cadence in Ionian mode is tonal, and not modal.
⚠️ Any cadences like V - I, IV - I, V - i, iv - i, or even rarer v - i will be viewed TONALLY, and NOT modally!
If you want to write a modal cadence, you should:
- Do not use a tritone in a chord. (Or else it is tonal)
- Avoid using the leading tone. (Or else it is tonal)
- Keep the character of the mode. (Use the characteristic tone in the bass of the first chord, unless if it is Dorian, which will be explained below)
In Ionian mode, the characteristic tone is on scale degree 4. So you will use the scale degree 4 note in the first chord of the cadence. The characteristic chords are in fact ii, IV, and viio. We would avoid IV and viio here. As Dom had mentioned, ii - I in Ionian mode is viewed more modally. It works the best when the first chord is in first inversion, while the second chord is kept in root position. You can also include the seventh in the first chord as well.
So in Ionian mode, the best cadence is ii6 - I, or ii65 - I if the seventh is included.
In Dorian mode, the characteristic tone is on scale degree 6. The characteristic chords are ii, IV, and vio. Avoid IV and vio. So we have ii available.
In Dorian mode, you would use ii6 - i, or ii65 - i. Notice I didn't put the characteristic tone in the bass of the first chord here, because doing so will create an unexpected 64 chord if it is a triad, and a 64 can only be used in certain circumstances.
In Phrygian mode, the characteristic chords are II, vo, and vii. The characteristic tone is on scale degree 2. We will avoid vo. You and Dom had mentioned the II - i cadence, which is great. There is also a Phrygian vii6 - i cadence. Notice both II - i and vii6 - i have the characteristic tone in the bass.
Therefore, II - i or vii6 - i is the best for Phrygian mode.
We have characteristic chords of II, ivo, and vii for Lydian mode, in which they all have the characteristic scale degree 4 note in common. Avoid ivo and vii here. Use the characteristic tone in the bass of the first chord.
In Lydian mode, we get II6 - I. But don't include the seventh, or else it will create a tritone.
Avoid iiio and v in Mixolydian mode. We have VII left. The scale degree 7 is the characteristic tone. Put it in the bass of the first chord and resolve it to the tonic.
In fact, we get a cadence of VII - I for Mixolydian mode.
Now, we are in the Aeolian mode. The characteristic tone is on scale degree 6. So we have iio, IV, and VI. Don't use iio or iv as using them will make the cadence sound tonal.
So, in Aeolian mode, we get VI - i.
Finally, we are in the Locrian mode. This mode is hard because the tonic chord itself has a tritone in it! The characteristic tone is on scale degree 5. We get io, iii, and V as characteristic chords. Avoid using V. The io can't be avoided because it is the tonic chord. So we will omit the fifth instead.
Therefore, in Locrian mode, we have iii6 - i(no 5th) as the best cadence.
In conclusion, we get overall:
- Ionian: ii6 - I or ii65 - I
- Dorian: ii6 - i or ii65 - i
- Phrygian: II - i or vii6 - i
- Lydian: II6 - I
- Mixolydian: VII - I
- Aeolian: VI - i
- Locrian: iii6 - i(no 5th)
I'll add an image below to show the examples: