TBH I think that the azir and gnar release being so close to each other is kindof a fluke. I think when riot announced they were toning down champ releases it was probably more like we are moving some champ release teams to reworks and we are not scheduling a champ every two weeks.
It seems more logical to say that they are going to release whatever the teams are working on whenever they are "done"
Now I've also heard that Riot uses SCRUM for their development model which can alter things drastically. If you know how this works than great, if not: http://en.wikipedia.org/wiki/Scrum_(software_development)
In any case, because the community of this game (the customer) is so drastically split down the middle over what they want on seemingly every issue. Or just way to eager to yell at riot for anything. The priorities that they see that they have to work to changes all the time. When they released braum and gnar a lot of people were up in arms about them not releasing new champs often enough. when they nerfed lee sin every one was mad. and then when they didnt nerf lee sin everyone was mad.
Honestly I think whoever has to prioritize what the different teams at riot work on probably has the hardest job there... Thats also probably why you dont see a ton of work being done on the reworks, people started raging when they stopped putting out new things in favor of the reworks.
Hopefully once they are done with the SR VU we can see a lot more work done on champ reworks, but we wont know until it ships.