when i came to the hp fandom there was already an abundance of brilliantly written fics online: every theme, almost every kink has been explored - from forced bonding to mpreg to creature!fic.
i think that makes a great difference. people who have been in fandom for more than five years surely had a different fandom experience where many scenarios didn't exist yet.
for me canon and fanon is a muddled mess. i don't often clearly distinguish it and there are fanfics that i somehow regard as canon.
after the last movie will have come out, there will be even more post dh fics which i find a bit sad. i do like many stories that are completely au today.
so even less chan, detention, etc., but more mature, older harry and maybe also more family fics, where harry and severus deal with james, albus and lily.
maybe with the fandom aging as well, there will be more fics that deal with an aged harry and severus. i'd like to see that.