I have always believed that Watson would accidentally discover that Holmes is trans ftm and would end up bringing out his studious side by secretly researching about the subject.
The thing is that I find it hilarious and very nice that I always feel Watson would end up clarifying his ideas on the subject and opening his perspective based on reading a lot of texts that probably say a lot of shit about trans people and every time he tries to relate what the information said with Holmes it was impossible for him to do so he ended up cursing the author in mood "tHIS BULLSHIT MY MEN IS NOT LIKE THIS, ACTUALLY HOLMES IS" -passionate explanation about the great human being that Holmes is-, in addition he ending up agreeing and applauding the authors that treat the subject in a more neutral / positive way. (?
In fact I feel that it also applies to any Holmes interpretation (gay, asexual or non-binary), the situation is the same: the values and "morality" of Watson that he learned from Victorian society is dismantled because Holmes is great and although exist certain things that Watson does not understand, he knows that by being aware of who Holmes is in reality, the respect and admiration he has for him will not change by discovering these traits that are only details of the complex and interesting person that SH is.
And yes then Watson realizes that he is madly in love with Holmes.
No matter what.