Its true that the rules for marking stress and intonation keep changing. as far as my knowledge concern its because the pronunciation of any language does not depend on any particular rule. Its dynamic. Due to this reason the rules keep changing.
I'm afraid it is not possible to talk about intonation rules. The way speakers use the melodies of speech depends on contextual and cognitive factors and there is no one to one correspondence between intonation patterns and syntax.
A very helpful approach, especially for foreign learners of English, is the one developed by David Brazil in: The communicative Value of Intonation in English.
For intonation of English and Chinese, please see my book chapter: Xu, Y. (2012) Function vs. form in speech prosody — Lessons from experimental research and potential implications for teaching. In Pragmatics, Prosody and English Language Teaching (J. Romero-Trillo, editor), pp. 61-76. New York: Springer.