Adjustable block size
So, would it make sense to increase block sizes at least for these intervals and decrease afterwards?


The key problem here is miners can introduce transactions in a block for free. In other words, miners can create lots of transactions with high fees for free. And there is no easy way to distinguish these transactions from regular legitimate  user transactions. Therefore, there is no easy way to measure the actual demand of unprocessed txs. This essentially provides block-space for free to miners and opens up DoS attacks. 


  Would such mechanism might help Bitcoin in a way ?


Such a mechanism would certainly be helpful, but as pointed above there is no easy to make it work.