The incentives are what they are. Sure some miner can play the role of 'attacker', and include a transaction that takes an inordinate amount of time to validate. My claim is that incentives are aligned to render this a non-problem.
Riddle me this: built off a parent of the same block height, a miner is presented -- at roughly the same time:
1) an aberrant block that takes an inordinate amount of time to verify but is otherwise valid;
2) a 'normal' valid block that does not take an inordinate amount of time to verify; and
3) an invalid block.
Which of these three do you suppose that miner will choose to build the next round atop?
Your question is poorly constructed because you do not define what qualifies as an "inordinate amount of time to verify."
Riddle me this: built off a parent of the same block height, a miner is presented -- at roughly the same time:
1) an aberrant block that takes an inordinate amount of time (e.g., one hour) to verify but is otherwise valid;
2) a 'normal' valid block that does not take an inordinate amount of time to verify; and
3) an invalid block.
Which of these three do you suppose that miner will choose to build the next round atop in order to maximize profit?