If there's a way to make something reasonably affordable to fit a planck, I would be all over this.
A kit with a handful of colour coordinated blanks would be awesome. I don't even care about legends on my mods, and since many people aren't even close to the "standard" planck layout, it's a good way to go.
Even better would be a standalone kit like Nantucket Selectric had. I think the usual situation where the planck requires a TKL "base" set + a 1u mods set leads to a lot of us just not being able to justify it.
I know I usually get almost ready to buy, and then bail when I realize it works out to >$3 per key that I'll use.