Probably won't work unless there is at least two shuttles travelling in both directions each day. Flight arrivals are staggered morning and afternoon. Assuming a six hour drive, that is longer than one driver should be on the road each day which means a driver will need to overnight in the city they last drove to. At least I don't want a driver that has been on the roads in this country for 12 hours driving me. Those arriving in the morning will have a significant delay waiting for an afternoon departure and those who miss the once a day shuttle will need to overnight waiting for the shuttle the next day. Most arriving PUJ will need to return to catch their flight home and the delay and inconvenience repeats itself.
Flights need to be enticed back to POP by ensuring that airlines are charged the same to land at POP or PUJ. Unfortunately, price parity alone probably won't be enough to increase landings at POP as the expat market is just not sufficient on its own to fill airplanes.
I suspect the only viable alternative is a scheduled bus that directly serves the route between PUJ and POP. It would also be nice if there was a more direct highway from PUJ to POP without having to go almost to Santo Domingo before turning north. For the time being, the only option seems to be to pay up about $250 for a private taxi. At least that option leaves when you arrive in PUJ and you don't have to wait around for some other public transportation option. I would never do the public bus option.
Get to the PUJ bus station and wait for the next bus. 3+ hours to Santo Domingo. Transfer to a second bus company. Wait for the next bus. 5+ hours to Puerto Plata. Easily 10+ extra travelling hours twice per vacation/stay. Longer than most direct flights even from far away places such as Europe.
Arriving in PUJ with a final destination in the Puerto Plata area is not a viable casual travel option in my opinion. I've said before that if I can't catch a flight home from POP, I'll have to move to where I can get such a flight. If I do someday have to make such a change, it will be hard not to factor in all of the very real inconveniences of continuing to live here which on a bad day could lead to an entirely unintended decision to relocate home or to another country. It should be of National interest and a priority for the DR Govt. to ensure that all of the major airports continue to service North America and Europe. Expats won't live in and tourists won't come to areas that are too convenient and costly to get to.
