The word 'today' is meaningless regardless of where the comma is.
One must not follow words but understand the mechanics of the process.
The thief could not have gone to heaven that day or at all. Here are the reasons why not:
1 Cor 15:22,23 says:"and each in his proper order, a first-fruit Christ, afterwards those who are the Christ's, in his presence"
No one could go to heaven before Jesus, as he was the Firstfruits. He died on Friday Nisan 14, and was dead until his resurrection on Sunday Nisan 16. He did not ascend until 40 days later. So that guy was not in heaven that day, because Jesus wasn't.
John 14:2 "In my Father's house are many mansions: if it were not so, I would have told you. I go to prepare a place for you. And if I go and prepare a place for you, I will come again, and receive you unto myself; that where I am, there ye may be also."
Jesus ascended to prepare a place for them in heaven, so no one could go before that.
Also John 3:5 says "Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God."
Baptism of the spirit did not start until Pentecost, 50 days after Jesus was resurrected. That guy didn't get the spirit and is not in heaven.
He is dead and waiting for Jesus to resurrect him to the earth as Rev 20:13 says.