Legends of Runeterra went into Open Beta not long ago, but some have already managed to collect enough cards so they don't need to craft new ones. Although it's still quite rare, little by little more and more players will reach this stage and start to want to save their Wildcards for the future, asking themselves the following question: How will the game deal with this accumulation of Wildcards?
The answer came from a member of Riot on Reddit: There are no plans to limit the number of resources that can be accumulated before a new expansion arrives. So, if you wanted to start saving today for the next set, you could do so completely free of any constraints.
AlphaLvSim goes one step further by assuring players that any potential changes to the way resources are used will be announced well in advance and won't come unexpectedly.
Another question arose on the same Reddit thread: what is Riot's opinion on the creation in the future of a new type of resource called "Legacy", which would be a Wildcard only valid for obtaining old cards. The question had recently arisen in Magic Arena, with the rotation and arrival of the History format, which contained all the cards available in the game.
For the time being, this type of resource shouldn't arrive in LoR. Indeed, developers don't think that such a system can be pleasant for players. Collecting resources takes time and passion, and any potential changes to earned resources will be made with extreme care.