Most Tesla models don't support bidirectional because they had free Supercharging, and also probably because having your car not full at all times is not always the best experience. Other brands like Nissan had always supported V2H and in fact it has always been a selling point of OG leaf that it could double as the Powerwall equivalent since back in 2012.

Most V2H systems don't support zero-interrupt automatic transition because it has no means to know if the perceived grid outage is accidental or intentional, and if intentional, trying to back it up could injure/kill electrician who commanded it. But if the system is operating off-grid, I think those can be configured to be always uninterruptible.

I don't think either of those are real concerns. The free supercharging did not overlap with homes that could be charged by cars.

Also, safe islanding devices have been very standard for at least 5-10 years. Policy 1: House watches incoming voltage, and turns off the breaker if the grid is down. House electricity + solar stay on; line to power company stays at 0V. Policy 2: Panels see that the house voltage is low, so they turn themselves off.

Policy 1 requires an electrician, but mostly just for permitting. I'd guess a good fraction of the people reading this could safely do it themselves after reading a manual. Policy 2 does not require an electrician or understanding electricity at all. It's how DIY balcony solar usually works.

As far as I can tell, the Leaf never had this in the US. The 1st and 2nd gen hard the hardware, but the chargers weren't there. And the 3rd gen has only announced V2L.

From my perspective, "zero-interrupt automatic transition" is not that important, but being able to have the system smoothly move between having the solar recharge the car and the car power the house during an extended grid outage is critical.