When "it's what my character would do" is actually true.

[Mastikator]

1) Eberron's cosmology/afterlife is not some kind of ideal to be aspired to. It works for their morally-ambiguous pulpy setting, but if it was the only or even the primary one for D&D, the game would be a lot worse off.

2) Traits, Ideals, Bonds and Flaws are powerful tools, but saying alignment no longer has value because they exist is a bridge too far. Alignment on your sheet represents an aspiration, and those aspirations can help you figure out how your character might act in a situation that doesn't cleanly align (natch) to your BIFTs.

2) Ideal represents aspiration, and is an order of magnitude more varied, nuanced, precise and detailed.
Alignment (if evil) can also represent drawback, but again flaw does a better job.

Alignment tried its darndest to do every job, it's your personality, your aspiration, your flaw, your side, your afterlife. It's overburdened.

1) using ideals for planes could absolutely work for great wheel cosmology. The dirty secret is that the great wheel is already based on ideal and theme. If you remove the alignment text then nothing would be lost, really. The blood war would still happen the way it does. Mechanus would still be orderly and full of robots.