Valve have reported, that they decided which theme that want to have at the next Dota 2 world championship.
It was reported on the website of the game Steam that TI7 sea waves will be changed for vaults.
This must mean that in this way Valve want to reveal the lore of Dota 2 world.
The theme of the next TI was announced so early due to the reason that Valve will hold an open competition of the works for the new chest with the vault's theme.
All the works can be published with a notch Collector's Cache 2018 by Dota 2 workshop. The deadline of publishing is 13 May (UTC -7). If you don't make items for Dota 2, you can enter the workshop to vote for any work.
Valve are likely to endeavour to create theme items, but there is no exact information about it.