Not really. It's exactly how it worked in 4E.
There are basically two situations where the rogue gets to attack on other creature's turns:
* The creature provokes an Attack of Opportunity by moving away without Disengaging. This is likely rare, and I'm fine with the rogue being good at punishing monsters for moving.
* Another character gives up their action to allow the rogue to attack. In this case, the action economy remains the same - it's just been judged that it's more worth the rogue acting again rather than the character whose turn it is.
Here's the definition of round and turn from the basic rules:
"The game organizes the chaos of combat into a cycle of rounds and turns. A round represents about 6 seconds in the game world. During a round, each participant in a battle takes a turn. The order of turns is determined at the beginning of a combat encounter, when everyone rolls initiative. Once everyone has taken a turn, the fight continues to the next round if neither side has defeated the other."
Turn seems pretty well defined - it's actually the definition of round that is vague.
Cheers!