Have any storage engines been removed in MySQL 5.7?
No.
A.2.4.
Can I prevent the use of a particular storage engine?
Yes. The disabled_storage_engines configuration option defines which storage engines cannot be used to create tables or tablespaces. By default, disabled_storage_engines is empty (no engines disabled), but it can be set to a comma-separated list of one or more engines.
A.2.5.
Is there an advantage to using the InnoDB storage engine exclusively, as opposed to a combination of InnoDB and non-InnoDB storage engines?
Yes. Using InnoDB tables exclusively can simplify backup and recovery operations. MySQL Enterprise Backup does a of all tables that use the InnoDB storage engine. For tables using MyISAM or other non-InnoDB storage engines, it does a “warm” backup, where the database continues to run, but those tables cannot be modified while being backed up. See Section 28.1, “MySQL Enterprise Backup Overview”.
A.2.6.
What are the unique benefits of the ARCHIVE storage engine?
The ARCHIVE storage engine stores large amounts of data without indexes; it has a small footprint, and performs selects using table scans. See Section 15.5, “The ARCHIVE Storage Engine”, for details.