In order to gauge the interest of the community, I'm posting a poll here to see what people think about it. If no consensus can be reached, then nothing will happen. Horikawa is not convinced, and would appreciate community feedback before making any changes to base-game content.
This suggestion was about the colour of the character blocks, namely Link and Luigi. With the addition of a number of new characters, it's been noted that making each character block distinct (so that the filter blocks can be easily recognisable) is increasingly difficult. I have noted that this is in part due to the colouring of the default character blocks, and how they are optimised for a small character roster. (As a separate point, it has always bugged me that Luigi's block is a washed out green and Link's in brown, both very different from their game palettes).
My suggestion was to make the following change to the colour palettes of the Link and Luigi switch and filter blocks:

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The left of that image is the current vanilla SMBX palette. The right side is my proposed change for SMBX 2.0. This would not only make the palettes better reflect the colour of the characters they represent, but also free up some of the colour spectrum for new character blocks, which will help to keep each character block unique.
The poll in this post will provide some needed community feedback on whether to proceed.
Of course, if you feel you have a better suggestion than the change I am proposing, then please do suggest it!