While I could see how the camping scenario might matter to a few people, I would personally rather have a couple mAh larger battery because of the slight physical space savings that I imagine eSIM brings.

Oh yeah, agreed. If moving an eSIM requires me stowing away a QR code with my backup phone then I'll gladly give up my physical SIM slot for more battery.

The associated esim app has free connectivity to complete the signup flow without wifi. It is obviously more convenient to download an app to your backup phone than futz around with physical sims you just have to remember to do so before you go camping.

Now you might retort aha! See! In a very narrow set of circumstances.. let me cut you off, look, you're going to need to remember to bring a paperclip or sim tool to do it the old fashioned way anyhow. So you're remembering something. If you're an amnesic lost in the woods you got bigger problems.

Besides, those are 2 grams of weight savings in my ultra light backpacking setup!

Would you bring a spare phone then? Sounds implausible. If you did, and it’s an emergency you can use a phone without a sim at all with the emergency network.

I actually do, it's always good to have a few back up essential things if they don't take up too much space. Every time I go camping/travelling I update my old OnePlus 3T (LineageOS is still up-to-date which is amazing) and bring it with me. If my iPhone breaks I can move the SIM card and still keep at it.

Agreed. Both wife and I need our phones for work connectivity, and it's a lot easier just to carry our old models in case one of ours dies on a trip. I'm not going to buy an iPhone while on a trip out of the country - they won't even have the models that support Verizon in most markets.

My old phone is still logged in to Apple, still works, still holds a charge. I'd like some eSIM system that was as convenient as "phone dies, pull SIM, put in old phone, boot".

In the UK most carriers also offer printed QR codes for the eSIM. These can be scanned more than once to activate it. So you can store that somewhere and scan it on another phone.

What happens if you scan it twice on two phones at the same time?

The last one to activate will get service. I think o2 allows 3 scans of the QR code.