It may not be the solution you want, but its about as good as you are going to get with Blizzard.
We are going on 12 years now, if they haven't figured out how to push more content out faster to stop the lull at the end it is not happening. Whether you like it or not, Blizzard has basically said with WoD and Legion that short or year long expansions are a pipe dream. Basically it takes them a certain amount of time to produce good content, and make the changes they need to make with classes. Obviously, if they would stop overhauling classes it might shorten things a bit, but I've about decided that is a pipe dream as well. They can't help but try and reinvent the wheel when it comes to classes every expansion.
So based on what Blizzard is telling us you aren't getting anymore content that probably what you saw in MoP, that is pretty much it. So you can space things a bit better so that you are sitting around for 7-9 months at the end, or you can continue pumping things out in 6 months or less and then sit around for a year at the end of the expansion.
You can decide how you want it done, or you can let basic grinds make a big comeback. or roadblocks like attunements, or any other host of things that have been removed over the years. Basically they now know ( and have said as much) that it takes X amount of time to make content. You can ask and keep hoping for more, but basically 3 raid tiers in 24 months is about it if you want big raids. If you go with smaller ones you might could push it to 4.
The answer is basically to pump out as much as they can and space it better. You may not like that answer or agree with it, but that doesn't make it less true.