Here's how it would likely have to work.
So by comparison, the company I work for ships around 1,000,000 boxes a month. We've grown tremendously and have really disrupted the industry that we sample. We make a ton of different box types. So box 14 is different from box 67 and so on. We might send out 20,000 "Box 14" in a certain month, and maybe 26,000 the next month. Each month the boxes are different and are sent to different people based on the items they've gotten previously. Who wants to get repeated items!? Also, their interests are taken into consideration so someone who just signed up with interest x, y, and z and someone who signed up with interest a, b, and c would ultimately get somewhat different boxes every month.
Of course this is all do-able because our product pipeline is nearly infinite for the industry we're in. On the other hand, the magic industry product pipeline is more limited and to create enough buffer for industry churn there would probably have to be a good 2 year pipeline of monthly products before starting.
Plus roadblocks that would have to be taken into consideration:
What if you get something in your box you've already purchased?
What if you get something in your box that required prior knowledge, props or gimmicks?
What if you get something in your box that you simply don't like to perform, i.e. coins when you do cards?
There are two ways of doing box subscriptions. Every month, all subscribers get the same selection of products. Or, every month products are allocated based on a survey of interests/skill level/etc. I'd say the set selection is probably more doable.
Also, the idea behind many subscription boxes is to send samples to encourage full size product shopping. Well, it's very hard to send usable samples re: magic so the items would have to be full size and likely also new release items to ensure people aren't receiving things they have already gotten.
Care has to be taken that it doesn't turn into a "trick of the month club", because that really is no longer a subscription box. Each month should be a surprise as the multiple goodies you're getting in the mail.
Theres a lot to think about, but it's a big big business when done right. My company has grown tremendously and now our Manhattan office is huge, all the fun start up perks included. So it can be a success when done right!