Apologies, just realised following is not specifically about Victron and regulatory issues but is following on from the discussion on permitted wiring methods.
Although the standard 15A single phase connector commonly used on 'portable' generators has only a 3600W limit, by having a 3 phase input socket and transfer switch used instead (with all three phases joined at the inverters mains output) you are now up to 32A per phase, giving a grand total of 23kW of legal and safe offgrid supply to the house
I hadn't thought about using a 32A x 3-phase cable/plug/power inlet tied together at the AIO's output. But it's a great idea.
I have one limiting factor however which prevents me from doing that, which I'll get to later.
I have the same Hager 63A x 3-phase transfer switch as that pic above but have the three phases on the generator/off-grid supply side tied together in the transfer switch to operate as a single phase output. That was what my original sparky did some years back when we originally set it up. At the time I had a single phase petrol generator and no off-grid AIO solar/battery to use as backup (still have the generator - a Yamaha EF3000iSE).
My transfer switch on the generator input side is supplied via a single phase 32 A cable/plug/power inlet. I have an adapter cord so a 15 A generator outlet can at least supply power via the 32 A power inlet if ever that was needed. The grid side of the switch is powered by the regular 3-phase grid supply.
My 8 kW AIO's output is connected to a single phase 32 A socket/cord which plugs into the transfer switch's 32 A generator power inlet.
I confined myself to an 8 kW AIO since I was using a 32A single phase connection, but an 11 kW or 12 kW single phase AIO using a 3-phase supply cable would be much better as we occasionally sail close to exceeding the 8 kW capacity, and have tripped the AIO's overload once or twice. I'm supplying two occupied dwellings and a large outbuilding, so it's a juggling act at times. I can reasonable manage our loads but not the cottage.
My problem comes when using the system in grid pass through mode (which is roughly half the time) as I have a 32 A per phase mains supply limit.
Since my AIO's AC input is single phase, it's grid supply comes from a single phase. So even if the AIO could supply 12 kW on the output side, I cannot draw more than 32 A (~7.5 kW) for any extended period when operating in grid-pass through mode.
It sucks as my main supply fuses are 63 A but I was required by the distributor to install a 3 x 32 A mains supply circuit breaker.
Still, I sorta wish I'd got the 11 kW version of my AIO so I could ride through the occasional brief draws > 8 kW, as a breaker is not going to trip immediately. 11 kW (very rare) would take about a minute to trip a regular 32 A breaker. Most forays would be more like 8-9 kW and not last for long and a breaker is going to let that go for quite a while.
It wasn't an issue when my elderly Mum lived in the cottage, but she has since passed and it's now occupied by a young couple who tend to have higher power demands. I have some load shedding automations but even those can't help if they are not part of the load.
If my main supply breaker was 3 x 63 A then I'd go for this solution. That restriction makes it very tricky.