I find this hard to relate to as a gay man, since us gay men happily exchange information about our penises (or other equipment) before meeting up. I think if it's important to you that your prospective partner has a penis or vagina, then it ought to be be possible to clarify this directly rather than making assumptions based on gender identity. If you find that it's not possible to do so in the current dating climate then, well, I'm sorry. But I don't think trans people are to blame for whatever is creating that barrier to honest communication. My guess is that there are probably a lot of other questions that you would like to be able to ask your Tinder matches but can't because of various societal hangups and tabus.

From the gay side of things, I've never had the experience of finding out that someone was trans only at the point where they took their clothes off. I find it difficult to believe that this is a common enough occurrence that it's actually causing people significant problems in their dating lives.