Yes, I think people need to remember that there are reasons why ships have grown in size in the past. The main reason is that before they would design the exterior of the ship first, and then later try to fit the interior spaces inside. Now they lay out the interior of the ship and then design the exterior around that.
So at least in theory, if they're doing their job right, concept ships should no longer be growing well beyond their original size specifications.
To be fair, there was a secondary reason why some ships have grown in the past, and that is because they realized later on that they needed additional interior spaces that they had not at all planned for originally. The biggest example of this is the Idris, where they discovered while building the story line for Squadron 42 that they needed several additional areas added (armory, brig, extra crew quarters, etc). This could still possibly be an issue in some cases (I think they recently said they had to add a level to the Bengal carrier so they could add a tram system?), but I think this is also less likely for newer concepts.
Basically, don't count on new concept ships growing significantly during the development process.