There is a small trouble with this method... The frequency/period changes with the voltage Vin. But with the period the waveform duty cycle would also be affected.
A good way might be to use the polarity control on the IDAC and charge and discharge the cap with a similar current. this would require the comparator to switch between two voltage thresholds. Changing the delta of the voltages would change the frequency. This would be a voltage controlled frequency which has a constant duty cycle.