EDIT: Shop is now open to everyone! Thanks for listening, Discord. I really hope it's not just for the holiday season <3
I think it would be in Discord's best interest to open at least some of the shop to non-Nitro users. This could include smaller things like profile decorations. I'm sure there are many out there who would like to purchase one or a few items, and are even willing to pay upwards of $8 for a bascic decoration, but simply do not want to buy a subscription JUST for those few items. Discord is missing out on quite a bit of money from these non-subscribers.
At the very least, I think would be more fair to either a) unlock the shop to subscribers of Nitro Basic, or b) have Nitro subscribers to be able to choose one shop item for free (either one from each category or just one item total), and have the rest behind the paywall, like someone else suggested in this forum.