Zirene brought up a super interesting point on his stream the other day which I would like to share here.
Basically, Marksmen are a type of champion, just like Bruisers, Assassins, Mages, Fighters, Tanks, etc. Traditionally, every lane has had to be able to play multiple types of champions as the meta shifts and changes. Top players need to be able to play Tanks, Bruisers, and even some Mages and Assasins. Same for Jungle and Mid.
The exception to this rule, for a very long time, has been the Bot lane role, with Bot players ONLY playing one type of champion: the Marksmen.
For whatever reason, Marksmen have ALWAYS been good and meta, creating this idea among ADC players that their champion type (Marksmen) should continue to ALWAYS be good and in-meta. This to me, and many others, is kind of crazy. Assassins have not ALWAYS been good mid, Tanks have not always been good in the Jungle or top, why should the champion type of Marksmen be any different?
I for one welcome the chance to let champions other than Marksmen go, and even excel at, the Bottom lane role.
Edit: I do play several Marksmen in ranked, and I still feel this way.