According to http://krismas.org/, Krismas is different from Christmas in that it takes the celebrating of Jesus birth out of the equation. Celebrating Krismas "is about giving gifts, especially those “from the heart”; it is about the magic of childhood; it is about peace on earth; and it is about goodwill towards humankind. It is about the universal truths of goodness that surround this time of year."
So, if it is not actually the celebrating of Christmas, but rather a brand new holiday then it wouldn't be based on pagan origan and it wouldn't involve the birth of Christ, I see no reason why JWs wouldn't be able to celebrate it.
What do you think?