I really like the idea of it being a pebble sink! Especially since you need sooo many vouchers to get the items from the shop.
I did read in another suggestion thread that even for pebbles it could still cause people to spend real life cash (to buy moonstones to exchange for pebbles), so in lieu of that, I do not know how many people would go that route, but just in case I did think of a few alternative ways that the lootboxes could be made available. (copied from the thread in which this discussion took place.)
1. everyone getting a free lootbox with every event
2. Lootboxes being a level up reward of the battle pass in the event
3. lootboxes being very rare but random drops when doing activities during an event (I would change this to extremely rare if they are available for purchase as well)
4. sitewide giveaways similar to the holiday snowcat
5. offering the lootbox as a reward in events (plentiful profiles for example)
There is definitely some balancing needed if the devs decide to include multiples of the ideas, because the idea of soft retiring items is that they become extremely rare but not impossible to get. Making them drops, and purchasable (without limit) and giving one free and getting one through the battle pass, might be OP. So this is not necessarily an and/and/and list, but rather just a list of potential ideas.