The iFixit App Is Here

Why do I need to signup to try it? Trashed.

Any reason for the native apps besides “we had the money”?

So, according to https://www.ifixit.com/go/fixbot, the paid "Enthusiast" tier includes "OEM service manuals".

Is this a sign that iFixit is going to gatekeep and start forcing you to pay for repair content?

Oh no!

Other than the "battery lifespan predictor", I don't see why this needs to be an app when it's all already available on website (and indexed by google search).