Where I live (Northeast), pretty much the only time where an extended power outage is a serious problem is in the winter. And that's because of losing heat. A Powerwall-like "UPS" that could handle some critical systems (basically my furnace) automatically is interesting. But any solar panels are likely to be under snow and ice.
Pretty much the only thing that's really a problem for me in a power outage is losing heat because the furnace loses power and therefore potentially having pipes freeze.
I think Tesla alluded to building heating elements into the tiles to keep snow and ice from building up, but I am not sure whether this is making its way into the final product. (Also unsure how this would play out in a snowstorm well below freezing temperatures).
I have an oil furnace with forced hot water. Basically, just need to drive the blower, maybe a pump, and some electronics. Not sure what the electrical draw of my furnace is but it's not a huge amount.
You're right that, if you have electrical heat, a Powerwall would be pretty useless.
Pretty much the only thing that's really a problem for me in a power outage is losing heat because the furnace loses power and therefore potentially having pipes freeze.