Yeah I noticed that you can have multiple eSIM profiles in the Apple Watch now. Since I have the eSIM and the physical SIM in my phone both activate, there is the option in the Watch app is add a second eSIM profile to the Apple Watch.. Granted you can't have two profiles activate at the same time, but still excellent.
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(The second carrier in this screenshot does not support Apple Watch, but if I put in my other carrier SIM in my phone it works perfectly)
Don't get too excited, you need to pay for separate Apple Watch lines as well.
It's not like you can have two iPhone lines sharing the same Apple Watch data plan; that's wishful thinking. You can't even have two same carrier (say AT&T) lines sharing the same Apple Watch plan.