Yes. I prefer something more lightweight. But SOAP is a protocol. What I propose are standards for common use cases that are not as general purpose.
Example, Facebook API allows querying, interacting with the social graph, profiles, photos, feeds, events, etc. These are use cases commonly used on photo apps, social networks, eventing, etc. But it's proprietary. Now imagine an open source standard similar to that but that can define such building blocks including other scenarios such as contacting a web site owner (about page, contact page), querying/posting articles to a web site, querying/doing transactions with products/services, etc. Once you go through all scenarios, then the problem that remains will be more about agents/authorities/reputation/security of allowing someone to interact with services. With better access for apps to interact directly with content by bypassing the current web presentation layer to avoid spam/fraud.
Example, Facebook API allows querying, interacting with the social graph, profiles, photos, feeds, events, etc. These are use cases commonly used on photo apps, social networks, eventing, etc. But it's proprietary. Now imagine an open source standard similar to that but that can define such building blocks including other scenarios such as contacting a web site owner (about page, contact page), querying/posting articles to a web site, querying/doing transactions with products/services, etc. Once you go through all scenarios, then the problem that remains will be more about agents/authorities/reputation/security of allowing someone to interact with services. With better access for apps to interact directly with content by bypassing the current web presentation layer to avoid spam/fraud.