I think there is a significant demand for some kind of system for automatically watering plants, whether in connection to a vacation or not. Of course it won't appeal to every plant owner but I believe it would be very successful if it worked well. No idea what a viable price point would be. I think it would be much more popular if one unit can service multiple plants.
With hundreds of potted plants in 6 rooms in my house and some in a shed, I would never be able to afford a system of watering automation, and really enjoy watering plants, so I'm not your target potential customer. But I wish you the best for this project. If you can figure out how to make it work, it will be very popular I'm sure. Others have tried and not yet gotten there.