DLC only needs to be bought once, across all accounts.
Just tested DLC with a local copy of Zelda (Picked up from Qisahn.)
- I have 3 accounts. Main account is Canadian (Better than US, cheaper), and I have two other accounts :Japan and Australian
- Purchased Zelda DLC on Canadian Account. Local credit card can be used on the canadian estore no problem. Also, I managed to merge my old estore banked credits from my 3DS.
- DLC is detected and can be seen as purchased from inside the game.
- Tested Disgaea 5 bought from the Japanese E store. Loads and plays fine in English with my Canadian account.
- I can play Zelda with my japanese account, but surprisingly, when I load up the japanese region e-store, it told me that i have already purchased the DLC.
It seems that DLC is tied to your console, or perhaps tied to a single account on your console but all accounts are allowed to access it. Not sure, I don't have multiple switches to try it out
There is one caveat : I'm assuming you can only purchase DLC for certain games if they are only released in certain regions (You can't purchase DLC using a US e store account if its a japanese region game only and not launched in the US, unlike Zelda which is released in all regions).
TLDR;
Create as many accounts as you want, in any region. Choose which region is the cheapest and buy your games/dlc from there.