I have some basic knowledge and experience in java coding language, and know how useful an arraylist can be.

An ArrayList is a part of collection framework and is present in java.util package. It provides us dynamic arrays in Java. Though, it may be slower than standard arrays but can be helpful in programs where lots of manipulation in the array is needed. ArrayList inherits AbstractList class and implements List interface.

An arraylist basically allows the ability to make one variable, that can hold a list of values, and you can search for a specific number on that list, or find the number of a specific value. I think adding an arraylist command (or scoreboard) to Minecraft, possibly in an update, could allow datapacks to reduce the number of scoreboards created to save space for the user, and could allow more advanced datapacks :D

Edit:
just did a bit of research and found the /store command actually seems quite similar. Is it possible to add custom dummy values to the /store command?

Edit2:
Also, can I put a scoreboard value into the number for a /store command? Example: /store storedValue[scoreboardValue]