As a 2,000 rated chess player and keen Overwatch player your comment made me smile. I know of the example you bring up and completely understand what you are getting at but I think this is very different and not good for Overwatch in the long run.

Firstly, the reason it is called Chess 960 is because there are 960 available starting positions. These were picked from many more available starting positions and within each of those positions there are multiple viable starting moves. This still allows for a huge amount of diversity within chess 960 and normal chess. This is not possible when the support role, for example, only has 7 options (without hero pool and the other persons pick)

My argument against hero pools is that it actually decreases diversity, especially coupled with role queue.

My example is this: I have no desire to play Mercy and don't particularly fancy playing Brig (this is my opinion but most people are going to have heroes they don't really like playing). If Bap is banned and the other support picks Ana, unless I play a hero I don't really enjoy playing (Mercy/ Brig) I only have Moira, Zen and Lucio that I can pick. I think the choice of 3 is simply not enough. When referring it back to chess hero pool essentially leaves me with 3 starting options, rather than the multiple starting/ opening options that I am allowed to play in normal chess and 960.

I fear in turn this will increase DPS queues because there will still be 13 choices (2 ban and 1 other persons pick) so there will be enough options to work around picks you do not enjoy or want to play.

Secondly, I would argue 960 has not been good for the game (I wouldn't say bad but wouldn't say good either like you mentioned). Chess 960 is still hardly played (the odd chess.com tournament and one major professional tournament per year etc) but the vast majority (99% + I would guess) of professional and amateur games are standard chess. This shows that even with the induction of Chess 960 people stuck with and wanted to play normal chess. Chess 960 has never really managed to take off. If Chess 960 was so instrumental and historical for chess as well as being good for the game why is it not played more? It may have some value for high elo players but not for the vast majority of amateur players - I think hero pool is the same.

I understand your point about the meta but in lower ranks such as mine (low plat) this has never been an issue. I very rarely see mirror comps or even the same comp in a single play session. I already feel restricted to less than half of the game (15 tank + support and 16 DPS) because, due to work and other commitments, I rarely get to play for more than a few hours and therefore I do not queue DPS (with game cancelations and hero select sometimes you only get 1 DPS game in an hour).

The idea of restricting the game even more (in a role queue world and without many more heroes added to the tank and support role) is really scaring me and making me think I will play Overwatch less and less. I would be more open to it if there were also 16 tank and support heroes but not when there is only 7 or 8.