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.
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.