Honestly, attacking someone who wants to write Sherlock as trans like it's some big let-down to the 'readers that might already be invested' just sounds like you're projecting your own distaste of not being 'warned' a trans character might exist in the narrative. There's plenty of canon compliant reasons why Sherlock might be trans (http://december1963.tumblr.com/tagged/trans-sherlock) more so than cis. It's no different to writing a fic with 'no flagged intention' where Sherlock happens to have scarring from working in the field for three years. A headcanon people often add! Not actually official canon!

'Issuefic'? Please, for your own benefit, go and reflect on why you think of trans people this way. Are trans people such an issue to you?