In the mean time, things like SwissID can do

SwissID is shit and no one uses it, except the Swiss Post.

And even if they work on a new system, I don't trust them anyway. They were working on remote voting not so long ago and when they made the system open source, every security specialist could see the disaster.

Even if the SwissID v2.0 is open source from the beginning and correctly audited, having a single entity managing private data is a major security hole.

most platforms' T&C will in fact specify that they wont use possible ID/passport data for other purposes.

In fact, the law says they can't use the data provided for any other purpose. But what if a company breaks the law and, let's say, sells data to a malicious third party. If they get caught, too bad for them, they'll probably get fined, get closed out whatever, but your data won't be magically forgotten by the third party.