you're right, photo and gravi-tropism dont usually fight each other. but your system seems like it would pit them against each other.Geotropism and Phototropism don't work against each other, they are separate. If you put an entire plant upside down geo tropism will make the bud grow up and the roots try to grow down which fucks a lot of stuff with bud plants. With my thing the plants would be growing more horizontally with the buds hanging down towards the light.
I'm not saying it wont work, I hope it does and I look forward to watching your grow progress....but I have a feeling you'll be stressing the girls a bit too much.