No doubt, this is the concern. I've covered most of my thoughts here
http://stratics.com/wow/wow-warlords...moving-forward
But to summarize:
They are being pressured from the top to make expansions faster. Ion and everyone else understands that if they are going to do a 1 year expansion, there could only be two raid tiers maximum.
But at the same time, everyone actually working on these projects realizes a 1 year expansion isn't likely. Adding more people makes things quicker, but its not exponential. Its not like you can have those 10 new people all work on the same barrel you are putting somewhere. Individual efforts still take place, and will always slow down the expansion.
In reality, the owners and higher ups will be delivered the bad news that the 1 year concept wont work, and we will see three tiers.
The scary part though, is that they must have already begun work on the Grom raid. Which means that if "things don't got to plan" then are we just going to get some random raid after it?
Its all quite murky, but nothing to be upset about. As long as they keep making raids as good as they were in MoP I will be more then satisfied.