Well, it depends, do you mean RTS for just the battle screen? Because my favorite 4X game, Sword of the Stars (The original) was that. Not to mention that is essentially Total War, too.
In fact I tend to think 4x games are made better by that element, especially if real world geometry of the unit, and how it attacks/defends, are made aspect of unit balance. For example, in sword of the stars, weapons which face forward were far more powerful, but they were far more difficult to use than broad sides. Just like how sword stats in Dark Souls could be deceptive because how the weapon moved in the world was important, having that element in a 4X game prevents it from being just a big case of rock paper scissors.
(The worst miss of all time was SoTS 2. It had everything, but they just didn't finish it. Armor had layers, and weapons had penetration templates, so some weapons did all four of their damage in a straight line, which allowed them to punch out armor, while others did their damage horizontally, which sucked vs armor but was really good vs internal components. Was really an awesome design concept, but the game sucked.)
In any case, if they say its a mesh between TBS/RTS, I suspect it just means the battle screen will have a pause button. (But RTS style movement has numerous advantages over TBS, the biggest of which is momentum becomes a consequence. Turning a ship or unit in a more RTS like environment, and having it be slow to turn another way can add a huge tactical layer compared to chess-like movement.)