but what if they DO repent in the very last second and you all have judged them wrongly???
There's nothing being judged other than the action. A refusal of burial is not a denial of heaven, nor a judgment on their eternal condition, but rather an affirmation that the action performed deliberately was not in accordance with the Church's teachings on the sanctity of life, and that the person didn't have the time to sufficiently repent & confess within their lifespan. However, we continue to hope and pray that the person is indeed blessed with a place in the Heavenly Kingdom, especially since our Orthodox spiritual tradition forces us to face the fact that we are indeed worse sinners than the person who committed suicide - if they're condemned for what little thing they've done, then I'm a goner for what I've done.
Just as a non-funeral is not a judgment that the person is condemned eternally, so too is a funeral not a guarantee that a person will find themselves in God's eternal loving Kingdom. Neither the presence of a funeral, nor its absence, usurps God's authority to judge the living and dead.
Take, for example, an Orthodox Christian who decides to marry a Muslim. They cannot be married in the Church - there is no such animal as an Orthodox-to-non-Christian wedding in Orthodoxy. That doesn't stop us from hoping and praying that the couple will grow in faith and love and will be taken together into His Kingdom - it's just us acknowledging that it doesn't follow the preferred path that Christ gave us. Same with volitional suicide: if the person was of full faculties and they committed suicide, we cannot sanctify the action through the funeral service, but we can continue to hope that they did find salvation in their last moments.
I pray for friends and family alike who have committed suicide; in the two closest cases to me (an aunt, and a college roommate/friend), I'm fairly certain, based on their own pre-death behavior, observations of others, and autopsy reports, that neither one was operating with a clear mind at the time they committed suicide. But even if I were certain that they knew what they were doing when they decided to end their lives, I would still pray for them, and have the hope that the Lord will forgive them. Again, if they're disqualified from heavenly joy automatically for their suicide (despite being more loving and compassionate than I), then I'm probably doomed.