Bidirectional foils are sinful and an offense to god and man.
Look, what's the actual argument here in favor of them? Foot switching is hard? Learning to foil takes practice? You already own a twintip and would like to add a hydrofoil to it?
So in order to meet those "needs" you're going to go ahead and disregard 100 years of aerodynamic science and computational fluid dynamics?
Someone already replied that wings don't work backwards. Do you think that's because they're just stubborn? Do you think that's because only idiots have tried so far and nobody who actually wants it to work has given it a shot yet?
Or maybe it's just a shit idea that defies science and should be eradicated because it's bad engineering coupled with a stupid inherent premise of trying to avoid learning how to foil correctly on real equipment instead of this bastardized nonsense.
One video of the person who has the most at stake (the designer) going back and forth slowly on a wobbly-ass twintip is not "proof of concept."
This is just wrong, and bad, and stupid.
But by all means, it's your money, use it however you think will make you happy.
Edit: One last point...Neil Pryde tried to launch a convertible twin tip that could be mounted to a hydrofoil with the CR:X class and the only feedback that stands out to me from the people who rode that equipment was that the board was way too stiff to be a good twintip and way too flexible to be a good foilboard; it was bad at both and good at neither.
Consider whether a flexy-ass twintip designed to load-and-pop is the platform you want to use to load up a foil that depends on rigidity to create stability.