I can’t speak too much to the price issues in the US, since I don’t live there. In other countries, epinephrine autoinjectors and glucagon kits cost about the same. And in most countries other than the US, these things cost significantly less (including epinephrine autoinjector brands like Emerade and Jext that aren’t available in the US). Also, the EpiPen is not the only autoinjector available in the US, it’s just the most well-known and the most expensive. Other brands, such as Auvi-Q and Adrenaclick, are considerably cheaper from what I understand.
The convenience of an autoinjector is probably worth it for anyone who lives alone, travels a lot, or works in a changing environment. I have a glucagon kit, but at the moment it’s useless to me for severe lows, because I can’t mix it up and administer it myself during a severe low and I wouldn’t expect colleagues (most of whom I don’t see every day) at work or strangers if I was travelling to know how to use it. The EpiPen, on the other hand (which I carry), is something I’d be able to administer myself during a severe allergic reaction or hand to a colleague or even a complete stranger and have a pretty good chance that they’d know what it is and how to use it.
Epinephrine used to be available in kits with prefilled syringes (which looked very similar to today’s glucagon kits) alongside various brands of autoinjectors in the '80s and '90s. There are companies working on nasal and inhaled version of epinephrine. However, unlike glucagon, if someone self-carries epinephrine and needs it, I can’t think of a situation where they wouldn’t want the full dose.
I think North America is the only place where Tresiba is limited to disposable pens. And I agree with you that that’s annoying, because I hate disposable pens. But Tresiba is produced in 3.0 mL penfills elsewhere, so it would be nice if this came to North America, or at least Canada where reusable pens are more common than disposable ones.
A company called Xeris, who has submitted for FDA approval of their autoinjector, is also working on a mini-dose pen and a pump-compatible version of their glucagon. Zealand Pharmaceuticals, the company mentioned in the article linked to in this thread, is also working on both an autoinjector and pump-compatible glucagon. Eli Lily has submitted for FDA approval of nasal glucagon. So I do think there will be multiple methods of delivery in the future.