And then what else would you need? The DBX having additional slots would render upgrading to bigger ships with more slots completely pointless for exploration. The DBX and the DBS are pretty much the entry level explorers, they give a nice little introduction to what it's like jumping long distances and honking at stars, but they are only entry level explorers and aren't meant to be the be all and end all of exploring.
If you want to fit everything exploration related into a ship for exploring, then that's what the Asps and the Anaconda are for.
If we had another half-dozen other oddities, scanners, processors and gizmos to install in our ships for exploration purposes, then it would be okay for the DBs to get a special scanner slot as they would still be very much limited by their internal slots, but until then any increases to the DBs' internals would simply render the bigger explorer ships utterly pointless for exploring.
The DBX isn't an introduction to exploration. It is a dedicated exploration vessel, but is not great at exploring. The Cobra Mk3, 4 and Type 6 are better explorers at a much cheaper price.
Infact I would go and say the Adder and Cobra are more entry level explorers.
Adding an extra size 1 internal slot would help the DBX as an exploration ship. It wouldn't be as good or as versatile as the AspX or the Anaconda, so people can still go up in to those ships.
As it happens I can't stand the AspX, and I don't like the big ships, so I am now exploring in a Cobra mk4. It would be nice to explore in my DBX which I prefer but doesn't have the internal space. They should also add more armour to the DBX. It weighs the same as an AspX but half the size. Where is all the weight. Yep, give it more armour and a size 1 internal slot and you have a good niche ship. The Combat explorer, not as verstile as the AspX but has nice combat capabilities.
I can see the AspX getting a size 1 internal slot as well.
DBX: Combat Explorer
AspX: Combat, Trade and Exploration.
That is fair. The AspX would still gets the upper hand in jump distance and internal space.