“Not sure how anyone could think animals could NOT go to heaven after reading Isaiah 11:6”
I’m guessing you meant NOT. God meant the Garden of Eden to be “heaven” - for Him to live with us (He walked among them). And before the fall - all of the animals and humans were vegetarian - the Lion DID lay down with the lamb.
After the fall, the first thing God did was kill an animal (a sacrifice as it were) to provide clothing for Adam and Eve (an act of compassion by Him). He also gave them permission to use and eat the animals.
I think the new heaven and the new earth will be very similar to what we have now - only perfect.
I’d be careful with the notion that the Garden of Eden was a sort of ‘heaven on earth’, unless you have a scriptural reference. God’s living with us doesn’t necessarily imply he intends to merge heaven with earth. After all, the verse only says he will make a new heaven and earth. What would be the point in saying that when he could have easily just said, “Look, I’m making a new heaven”. Only then could you infer heaven and earth would be merged. Just because God walked with Adam doesn’t mean Adam heard anything more than footsteps and felt God’s presence. I’m leaning towards the literal interpretation that in the beginning there were two realms, and Isaiah talks about two realms in the future.
What a gentle and loving thing for Our Father to do when His children had sinned! A little thing, often ignored in the light of Our Father's Old Testament swift justice, but so fatherly nonetheless.