That invitation is issued by the Archbishop of Canterbury, not by some of the guests deciding who is acceptable. It also flies directly in the face of the earliest worries about Lambeth, that the Conference might indeed become a Council and might try to determine by whatever means necessary correct doctrine or discipline. The Conference could adapt certain resolutions that would provide a litmus test for future inclusion in the Communion. The Kuala Lumpur Report is touted as a possibility. This is dreadful.
Litmus tests are reactive in the worse way.
Barring other possibilities the idea of a walk out has been floated as a means of political coercion. If the threat were taken seriously the West would have to clean up its act and repent. If not, so be it. And here the danger is simple and real. It assumes that these bishops are not themselves subject to judgment and repentance, or that their own houses are powerfully in order.