There was WAP, which was kind of the ancestor of AMP. It wasn't terribly popular then either.
I feel like while they were inspired by some concepts from there, the biggest contributor to the idea (apart from the need of locking in people in one 'easily acessible' platform) was opera's OBML format/protocol which was really decent at the time and provided a lot of benefits AML is marketed for. Probably the only problem with it was the lack of any interactive javascript, and that where it failed to meet adoption. Oh, but well, it was really niche as well, that did nothing good too.