It's sad that the Beta Focus Group project hasn't been successful as the Beta market doesn't (and can't) fulfill its role at this moment. I think 90 % of players aren't interested in hunting of bugs or providing some feedback.
This might be true, but as this is an international environment, there might be many cases where you might see 3-4 people reporting bugs all time but they may not be the ones that digged them out. Others who are having issues expressing themselves in english are just mentioning issue and other person reports it.
Also apart from forum we also have ticketing system for buqs reports and there we have no clue what is going on.
About the world, there probably should be one or two longterm worlds with settings similar to live market ones. For hunting of smaller bugs which can occur after an ordinary update. For new features, a new short-term world with fast (e.g. speed 30) speed could be fine.
I assume that all should be long term worlds but there should be a change on schedule for features/updates going live to production.
Bug hunting or small bugs will can be located regardless speed.
On the other hand for new features (i.e. pass from ver 1 to ver2 or introduction of new hero or god or any other "big" change or a new event) I think ther ebe a period of 1-2 weeks for testings in beta servers and then go to production servers (live servers) because now I have a feeling that they go live on next scheduled weekly update i.e. time for beta testing is far too small. and also keep in minds that this is voluntary job and user might have other IRL activities, so higher speeds will not help on this case.
Another issue can be English... there is no Beta enviroment for players who speak just in their native language. I also believe, there should be some reward on their live market account if they find a bug or post a constructive feedback.
Local market beta servers would be great but has some "bugs" as an idea. It is more costly (hardware wise and also free coins), also people might prefer playing on the beta so as to get new features sooner....
As for the rewards, I recall couple of years ago where there was an amount of gold coins as a reward for locating bugs but not sure if this is still on.