1) JPY is one of the cheapest currencies on earth, while CHF is one of the most overvalued.
2) I think gold will face headwinds due to the rising real rates of return on currencies in the coming years, CHF being a major exporter of gold should feel some of that pressure
3) The market has a BOJ priced in, and I believe the BOJ's next step isn't likely to be more than they are now, which would mean that eventually, the market will need to price in some tapering on BOJ's behalf.
4) SNB will be wary to make any moves that are interpreted as hawkish, as the overvalued CHF has already been affecting the Swiss economy.
5) short positioning in JPY is extreme, while short positioning in CHF is reasonable
6) These are both "risk off" currencies, so the dynamics that drive this pair should be uncorrelated to the rest of my book.
This trade lacks an immediate catalyst, but an immediate motivator in this pair is likely to be unexpected.
Morgan Stanley also recommended a similar trade in CHF/JPY recently, here is their reasoning
Credit to my friend for analysis this setup