From my experience, a late diagnosis did not mean milder lung disease. Although I do not suffer from any digestive problems, thank G-d, I do have moderately severe pulmonary issues.
My last FEV1 was 39%. It's usually around 49%. I'm on IV antibiotics right now, hoping to get it back to near 50%, please G-d.
Although I had persistent lung, sinus, and "other" problems all my, I was not diagnosed with CF until the age of 63. Sweat tests were always negative, which is the case in a small percentage of people CF and particular mutations. Genetic testing did not exist, and/or it was not what it is today. I was being treated for persistent lung infections and Bronchiectasis for many years before the CF diagnosis.
To answer the original question, I would be quite surprised if there wasn't a "cure" for CF and other genetic diseases in less then 10 years, please G-d.
Stephen
70 y/o with CF (D1152H, G542X0) and Bronchiectasis