it was a bit early to declare that the SMS URI scheme was finished. another iteration was required, this time an update to version
draft-wilde-sms-uri-20. the main reason was that the draft did not contain any information on how to compare SMS URIs. Section 2.4 now explains how to compare SMS URIs (mostly based on the definition of how to compare to tel: URIs), and (once again...) hopefully that was the last change required before the draft can be published as an RFC.
this is a really long process, but on the other hand it is really good to see that people care enough about this to take a close look and comment on the draft. thanks for all the comments!