Pico Day has really evolved over the years. It used to be dedicated to the original Pico cast, then expanded to include al the core NG characters (and staff for that matter). The next logical step is to make it evolve further into a day for fans to submit parodies and tributes of their favorite NG characters and users.
I would much rather see holidays dedicated to outdated characters and groups go to pasture. You just can't justify dropping/replacing Pico day and keeping shit like Clock day that caters to memes that have long passed their twilight, or even madness day which says we care about that one franchise more than all the other great ones that have no day.
Keep Pico Day and make it more open and we'll still get all the great madness movies and games, and the clock crew will always have a presence as well.
Then you can come up with new theme days to fill the months with lame holidays. Stuff that's themed but not restricting, like the much under-promoted Robot Day.