I guess, in that system the estimated queue-times for people not opting-in for arabia nor arena will be around factor 3-4 of what it's now.In the opt-in systems queues are linked to maps. So if you selected Arabia and Nomad then you will be in both map queues and wherever the most suitable match found first, thats the map you get.
Almost every proposal made in this thread (opt-in, unlimited bans etc.) will have an unpredictable (but definitely negative) impact on queue times, especially for people who don't like to play standard maps, because they all require breaking up the queue into several separate map queues.