I don't know, I'm not seeing it as being as simple as 'tomboy = lesbian'. This is something that's been building with Kat since... well, in a direct way since Faraway Morning, but even in an indirect way as early as this page (http://gunnerkrigg.com/?p=111) of Of Old And New. And Kat WAS actually presenting as more feminine there - she had slightly longer hair, and almost exclusively wore her school uniform and its skirt. (Note Kat's almost luminescent blushing!)

Er, plus, I'm not entirely sure Kat's a lesbian. Quite possibly queer in some way, but possibly being attracted to girls doesn't actually invalidate her past relationship with Aly, or her crush on Eglamore. She's most likely bi. (Also, Annie DID dream about Jones, naked, in a rather similar scenario to Kamlen. She could well be bi without it being SUDDENLY, QUEER.)