Probably, but I have no idea what the limitations are in iOS that have kept something like that from being built already. Not a dev here, just a power-user and one that only uses Android for mobile these days.
There are a lot of ideas about what the ideal onboarding experience should look like. I think they will all be tried and we will narrow down on which is best based on how well received they each are by non-technical users.
I've thought it would be a great idea to have a signer built into a password manager, like Bitwarden. However, there are a LOT of people who still don't use password managers for some reason. (What is wrong with you people?)
Others like the idea of building it into a native client on each device, such as Damus on iOS and Amethyst on Primal, etc. Perhaps all native Nostr clients could have it built in, and users would just choose which one they want to use for it. I think this would create artificial lock-in for whatever client they chose. Yes, they COULD just set up a different client as their signer, if they wanted to switch, but most would just see this as an enormous hassle, especially if they have remote signing set up with multiple other clients that they would need to set up all over again.
Another idea I have seen that would possibly work on Android, but could never work on iOS, is to have the signer built into a Nostr app store, so that the user would use the app store for their original onboarding and for finding apps to use with their signing credentials. Over here on Android, that would maybe mean nostr:nprofile1qyv8wumn8ghj7enfd36x2u3wdehhxarj9emkjmn99uqzqun2rcnpe3j8ge6ws2z789gm8wcnn056wu734n6fmjrgmwrp58q390rp63 adding it to nostr:nprofile1qy2hwumn8ghj7un9d3shjtnyv9kh2uewd9hj7qghwaehxw309aex2mrp0yhxummnw3ezucnpdejz7qghwaehxw309aex2mrp0yh8qunfd4skctnwv46z7qpq0r8xl2njyepcw2zwv3a6dyufj4e4ajx86hz6v4ehu4gnpupxxp7sdvr7w9 . I think he has more ambitious goals than just having Nostr apps in his appstore, though, as can be readily seen by perusing what is already available there.
Personally, I think having it as a separate app, like Amber, is just fine. I would love to see that signer app actually become the app used to onboard new Nostriches, and then suggest to them clients they can use with the signer, and how to get Zapstore in order to find more. However, for that to happen, the signer app needs to be readily available in the system's main app-store, otherwise you are expecting newbies to download it directly from GitHub or first get Obtainium or Zapstore (ALSO not available in the Google Play Store) to download it.
Flow should be: Go to app-store > install signing app > set up basic profile > back up nsec now or skip till later > select client to try and be redirected to download it > open client and main option for login is using a signer app which automatically reaches out to already installed and set up signer > be amazed because the client you just logged into has your profile information and a default feed because you haven't followed anyone yet.
