I'm using
ADS1248, but quite an old IC and different from your application.
Seems like neither TI or digikey have gpio as an option in their parametric search. Probably due to it being an oddball feature..
The thing is, it would be very easy to find an i2c GPIO IC driver. I'm not saying writing one for the ADC is hard, but, most likely you will need to write it yourself.
So in the end it can be less programming work to use a common part.