We don't have enough housing or mass transit for the first option, and building more batteries has proven significantly easier than building either more housing or more transit.

This is where we'll have to disagree - the limitations to building housing and mass transit are mostly economical, while for batteries they are mostly physical.

Would definitely disagree on that. The limitations of building housing and mass transit are mostly political, while for batteries they're both economical and physical. I'd take physical problems over political ones any day.

We know we can't quickly replace all gas combustion engines on the road today with batteries because of material supply constraints alone. However if the goal is to reduce carbon emissions by vehicles by 90%, we can probably get there by replacing 95% of all gas-only vehicles with plug-in hybrids, which require a small fraction of the amount of battery material than fully electric cars require. I'm probably off with my estimates, but I believe they're in the ballpark.

Hmm, that's interesting - I thought that hybrids were less efficient, but maybe if they also require much less batteries they could be a great stepping stone ?