From a purely fun point of view I don't see too many issues besides how this gets implemented (e.g. role queue means way longer queues, no matter the numbers involved), as in the end everyone surely has an hero (or more) he/she likes to play, this should make it easier to actually play them and not being forced on something you might be even good at but really don't want to play.
From a competetive point of view... well the opposite, but then it's again a personal issue you'd still be free to decide if you want to have more fun (while still trying) on your fav heroes, or if you ONLY want to win no matter what, then nothing would changed compared to how the game is right now.
In the end this won't remove trolls/throwers/OTPs, it will only remove GOATs, and that's why I'm neither happy nor mad about this change... Maybe it's 'cause I'm not a DPS player.
Last point I have is a very personal opinion... I have the feeling this will lead to longer periods where a meta isn't established (unless OWL and other heavily organized teams will actually spend time trying to create/mold one), but once there the new metas will be even harder to break, so not so sure this is an improvement.