I am aware that the Eastern Orthodox do not have the filioque, and I even readily admit that it is not present in the earliest versions of the the Nicene Creed.
Nevertheless, anybody who understands the rest of the Nicene Creed (leave alone other orthodox rules of faith, such as 1 Peter 1:11-12) cannot contest that the Spirit proceeds from the Father only by the mediation of the Son.
The filioque is orthodox primarily because the opposing view—that the Spirit proceeds independently of the Son—is heterodox. The more-primitive version of the Nicene Creed could have left room for another creed, to correct a future heresy that affirms that those who are not in Christ may have the Spirit (completely contrary to, say, what is affirmed repeatedly in the Johannine and Pauline epistles). Alternatively, one could just incorporate the filioque and be done with it.
If anyone says that the filioque is not orthodox, may he be anathema.