Over in the "Large residential service question" topic, using 208Y/120 three phase was mentioned for mega mansions that have a massive service drop. Often this is a utility requirement due to the limitation on single phase service, sometimes in some places as low as 200 amps, though usually at least 400 amps.

I have experienced multiple complications due to the higher voltage changing from 240 to 208. Among these is lower heat from resistive devices like ovens, and motor burnouts. I'm wondering how these things have been dealt with in cases you might have encountered.

Another issue in upgrades is conversion of existing single phase panels to three phase.

My grandfather got three phase power to new his home around 1960. The purpose was to support some three phase equipment in his wood shop. But it was all on a single service, so the house had 120/208V as well. I don't remember if it had 2 of the phases or all 3 running in the house directly. I do remember that my grandmother's electric stove was slow to heat up, and this had been complained about as an ongoing problem. One year, there was a brownout in the summer. Being already on low voltage at 208 volts when intended to be on 240 volts, the brownout caused the air conditioner to burn out.

I believe he was expecting to get 240 volt delta with center tap and ended up with 208Y/120. He had trouble with some of the woodshop equipment, too.

One alternative I see is "triple split phase". That is, 3 separate 120/240 volt systems. It would be derived from an ordinary 3 phase supply by 3 single phase transformers. Each is then fed to their respective panels. You'd have to keep these 3 systems reasonably balanced.

Another alternative I see to keep single voltage 2-wire 240 volts stuff running well would be to buck-boost the 208Y/120 system up to somewhere near 240Y/139 and operate line-to-line from that to get 240 volts, possibly on a per-load or per-circuit basis with small transformers.

Mega mansion owners often get "industrial style" appliances, such as for the kitchen. Many of these are either the exact models, or domestic variations of models, intended for commercial/industrial use. So these might already be adapted for 208 volts, such as 208V heating elements for water heaters.