Why does START TRANSACTION WITH CONSISTENT SNAPSHOT not work with SERIALIZABLE isolation level? The MySQL doc for START TRANSACTION says:


  The only isolation level that permits a consistent read is REPEATABLE READ. For all other isolation levels, the WITH CONSISTENT SNAPSHOT clause is ignored. A warning is generated when the WITH CONSISTENT SNAPSHOT clause is ignored.


I'm surprised, as I thought that the SERIALIZABLE isolation level, being above REPEATABLE READ, would also offer a consistent read.

What prevents WITH CONSISTENT SNAPSHOT from working with SERIALIZABLE transactions?

I even found this bug report from 2012 where the doc originally said that this worked with both REPEATABLE READ and SERIALIZABLE, and they explicitly changed it to REPEATABLE READ only, so it looks like there is a technical reason for this. I tested it and MySQL does generate a warning when used with SERIALIZABLE.
The WITH CONSISTENT SNAPSHOT modifier starts a consistent read for
  storage engines that are capable of it.
  
  consistent read A read operation that uses snapshot information to
  present query results based on a point in time, regardless of changes
  performed by other transactions running at the same time.


With SERIALIZABLE isolation level you don't need to use a snapshot because all necessary data is already locked by your transaction.  

SERIALIZABLE isolation level should be more ACID compliant than REPEATABLE READ because the second one allows non-locking reads which may lead to a violation of the I (Isolation) rule of ACID.