> is SpaceX actually worth $1T

Actually irrelevant to an index calculation. If your index manufacturer is taking this into account at any level, they're actively managing. S&P predates the modern active-versus-passive dichotomy, but it functions within it in practice, and despite being a leader of committee-based indexing philosophy, they've broadly found success by also being champions of passive management. And part of doing that is rejecting judgement over how the market is weighing this or that.

Historically a $1T market cap with a PE of 20.0 would be achievable with a $50B/yr profit. That seems easily achievable eventually for SpaceX, as it has actual hardware and services and IP.