Seems as if this isn't going to happen. Many players have been wanting the cap lowered for these instances from 10 to 5, because the dungeons are designed for a 5 man group rather than a 10 man. Caydiem responded to the gripes...
I seem to recall this discussion came up among the developers around the time Dire Maul was set to be released and the caps were first instituted. There were many people weighing the pros and cons of limiting Stratholme and Scholomance to the number of players for which they were designed (five).The outcome was the ten-man raid situation you see today.
Having the ten-man option available helps include more guildmates if they want to go on a dungeon run. It allows for less set pieces to rot/be disenchanted. It gives newly-60 players a chance to learn how raids work and where their role lies without harsh and frustrating consequences.
Let's look at Dire Maul. DM is a five-man only dungeon, and if you're not on the ball, the potential wipes can be pretty devastating. The learning curve heads sharply upwards after east wing, and a fresh few 60s who are not entirely certain of strategies can have a difficult and aggravating time in the Highborne wing. DM (north and west wing, anyway) has always been for the more skilled level 60s who know their class and can act quickly in a variety of different situations.
I understand where you're coming from on Stratholme and Scholomance, but as far as I'm aware, there are no plans to institute five-man caps on those dungeons.
