With Google Fi you just sign into the fi app and transfer the phone. You need wifi but that's it.

yea, that's my biggest annoyance with it, if you can't pass security on the phone (talking to you prepaid carriers who have absolutely shit CS and protocols) you can no longer just hot swap the sim to get your verification code. You are just locked out of your account now. It's nice that it's more secure but, also such a pain in the ass for people who don't call their carrier a lot so they don't know their security.

Don't you need a SIM for calling?

Tbh I think you effectively could, but it would technically be your provider issuing a new one.

For me I just log into my provider's online account screen and I'm able to scan a new QR code

I thought you could too but I use Google Fi and I just log into my Google account on a new device and it lets me deactivate the old phone and download the sim to the new phone.

You get a QR code for the new sim, go into the eSIM manager on the phone, and scan it

that doesn't exist

Well fwiw, the post we're commenting on is about that now existing.

the ability to take it out of one device and put it into another one, effectively disconnecting my identity towards the network provider, from the handset

Unless you think that taking a SIM out of a phone means that the phone is no longer connected to you, which isn't the case at all. A phone's IMEI is sent along with the SIM data as part of the initial handshake to make a mobile connection, your carrier knows the make, model and serial number of every phone you've ever put your SIM card in. The police in most countries make them keep track of which cell towers that combo of IMEI and SIM connect to and at what times. There's no privacy in using a mobile network you pay a bill for.

that's not secure

Obviously this isn't the be all and end all of security, but an eSIM slightly improves device security because a thief would be unable to remove it and disable any theft tracking measures which require network access. (Yes I know about EM shielded bags, but most thieves are opportunists)

The only real advantage of a physical SIM is that if you smash your phone up, you can walk into a shop and put it into a new phone without needing an internet connection first. If I smash my phone up, I need a WiFi network to hook my new phone up to the network. On the flip side, if I get robbed abroad, the process is the same. With a physical SIM it's gonna get sent to my home address.

From a corporate device perspective it's an interesting evolution though, since we can remotely provision an eSIM through our mobile device management platform. No SIM to handle from the user point of view, and they can't take it out.