Most likely. I think they want some of them to be something you only got as part of that event. They played with that idea at launch, but back then they had a disclaimer on the receipts of event boxes and on their website that ALL skins would be available for purchase using tokens.
So they were forced to back down and make that year’s summer game skins availble for tokens the following year.
I think now that hasn’t been a promise in a long time, they are trying it again.
Based on everything we know, these skins ARE EXCLUSIVE TO BLIZZCON. If you want them, do not hesitate to get the 2019 Virtual Ticket. See this thread for details: