For starters, the x Alisaputrana hybrid has been in everyone's imagination because pictures of it have been floating around for decades.

As for horticultural hybrids, well it's always a matter of what is in flower at the time of the opposite gender. Nepenthes pollen does not store well at all in my experience, so you really need a male and female in flower at the same time, or a male slightly before hand. So hybrids are made with whatever is available at the time. I haven't heard what the rajah that flowered last year was crossed with (if anything at all), but I'm sure the seedlings will start floating around the market next year sometime.