Aside from being a trend, pan can be a shorthand way for some people to indicate they would accept a partner with mismatch of genitals, ie they would be open to dating a trans woman with a penis or a trans man with a vagina.
Not all bisexuals would.
Correct. I date women, and I date men. I feel desperately sad for anybody who feels they were born in the wrong body, I know and am friendly with half a dozen trans men but I have no interest in having sex with trans people.
Some of the trans women I have met have been so damn incongruous that I don't feel safe around them, in the same way that coming across a stranger in the street who is acting weirdly and appears to have a mental illness or be on drugs feels dangerous to be around.
Others I just feel sorry for, because they seem lost and desperately grateful if you will treat them with human dignity.
None of them I've wanted to shag. I like my men and my women to be at least sure of themselves, and kind people. All of the trans people I've met I've either felt scared of their behaviour, or wanted to motherly protect (wanted to, not acted that way unless appropriate before anybody starts).
If I'm honest I'm still unsure if this makes me transphobic. I'd be sad if that was the case, but I'm also old enough and secure enough in myself not to feel the need to adjust who I will sleep with to please others.