This would help serious players with tournament preparation.
When building the deck, rather than having to save multiple copies, you could just click the saved siding pattern for “Yummy”, or “Dracotail”, or “Going First”. This would make deck building faster and more intuitive, as you can more easily view a shuffled deck and do test hands post-side. Best case scenario would be unlimited slots, and you just press a “+” icon to add a new siding pattern, or an “x” to remove an existing one.
But Neuron’s system would work too, where you simply have 3 slots to work with, if that’s easier to implement.
This could be implemented into actual gameplay to make side decking faster.
My primary use case would be for actual deck building, however. Makes it super easy to check your decklist has a good gameplan for all the expected matchups. It also makes it easier to identify matchups your current list would struggle against, which ultimately helps you make better choices when building both main and side decks.
PS: If a deck change would compromise a side-pattern, you could simply delete the side pattern, and maybe have a pop-up explaining this to the user