I don't think having an heir is proof of anything very much. Certainly not proof he would have wanted the NT to do this. Plenty of people don't procreate (and some notoriously otherwise-inclined people, such as Oscar Wilde, do procreate).
I'm saying it's anachronistic to apply terms like 'gay' to people who lived in times where the term (and the reality it describes) weren't in use.
We can certainly talk about histories that are of interest in a LGBT context. I can think of various places (Sissinghurst, but also Anne Lister's home) that would seem suitable - because their owners left us enough evidence to suggest that they were interested in making their sexuality visible and were conscious of it being a same-sex sexuality. Even there, though, I would shrink away from slapping on anachronistic labels like 'gay' or 'LGBT'.
The problem with a term like 'gay' is that it describes a reality that might be totally different from Ketton-Cremer's actual life or feelings about that life.
How do you know if someone is gay? They have sex with men? Well, so did many Ancient Greek men who saw it as an entirely routine part of every man's sex life and entirely compatible with sex and marriage with women. They form intense relationships with the same sex and discuss how physically attractive those other men are? There was a huge fashion for this in the 1920s (not coincidentally, just after WWI), and many men did not see it as anything but an aesthetic and affectionate practice.
It's really hard to know how to interpret the sexuality of someone who lived in a different time. To take clues and say 'oh, they were clearly gay' is fundamentally wrong, especially when that person might find it upsetting or hurtful. We must remember that, even if we all think being gay is perfectly acceptable, it may have been a source of real shame for this man, and not how he would have wanted to be remembered.