If the Saints are alive, as we believe they are, then they are praying for us, and this expectation is not outside of the confines of the Christian faith.
But I must agree with you, FK, that we have no biblical evidence whatsoever that saints intercede on our behalf, and specifically in resposne to our prayers.
I never pray to Theotokos or other Saints. I do thank them, whether they can hear me or not, for being the role models for us to follow and for their sacrifices.
John wrote Revelation not Paul, and John refers to the prayers of the Saints. Did John (or any other apostle) ever refer to the saints as living as St Paul does?
Here is one strong example that the saints intercede,there are others
"When he took it, the four living creatures and the twenty-four elders fell down before the Lamb. Each of the elders held a harp and gold bowls filled with incense, which are the prayers of the holy ones". (Revelation 5:8)
I think that Revelation 5:8 gives a good indication that the prayers of the saints (on heaven and earth) are presented to God by the angels and saints in heaven. This shows that the saints intercede on our behalf before God, and it also demonstrates that our prayers on earth are united with their prayers in heaven