I see Sailor has recently announced the release of four new ink colours in the Shikiori product line:
Source: Sailor Pen website
(It's a little confused.)
Source: Sailor Pen website
The ink colours for Spring and Summer look pretty ordinary to me. The one for Autumn looks a bit like Rohrer & Klingner Scabiosa, and the one for Winter has that subtle shading-to-a-warmer-violet thing; but overall, I'm not so impressed by what I see, to be chomping at the bit to pay Sailor's asking price for a 20ml bottle of any of them.
That said, if reviews of Potsupotsu shows that the ink has good water resistance — where similarly multi-hued Diamine Bashful Blueberry doesn't — then I might be convinced to part with money.