First, correctly balance all the current ships - since ship launched fighters means we dont need to have big ships behave like fighters.
Then I'd like to see the panther clipper added as an alliance big ship - consisting of what amounts to two chieftain-esque hulls that are connected by telescoping pylons to eachother. Hardpoints out, they expand apart, hardpoints in they retract to fit in the large docking pads and mail slot. The panther clipper would be a defensive vessel with optimal hardpoint and cargo scoop placement for mining and turrets (huge turrets would be exposed on the center pylons when hardpoints are out). Not fast, but it's core internal modules and fsd would be well protected (hard to get a direct shot at). You would need to rank up with alliance military to acquire it. It would have very good shields and the necessary systems to power them and turrets - hardpoints would be placed in a way that make fixed weapons somewhat useless to enforce it's defensive role and avoid making the ship overpowered.
Also, an Anaconda MK2 (MK1 is pretty old)
Military support variant. Hull mass is increased over the mk1 - this increase is embedded module and hull reinforcement modules that can't be removed and provide better protection and energy use than user defined modules for the mass added. Jump range is thus dropped 33%. Less internal modules due to the added re-inforcements (1/2 of the potential storage capacity of the mk1). The mk2 has 4 additional utility mounts and 4 additional large hardpoints all towards the rear of the ship. These will be intended to be either turrets or missile launchers. Default armor is military. Cost of the base model ship would be at least 600 million to adjust for credit inflation. The intention for the role of this ship is that you would equip the hardpoints so that you could select the optimal type that is effective against any given foe at will, rather than having the energy to use them all at once (which you wouldn't at max sizes). Would require a slight change to power management so that via a hud toggle, hardpoints not under the current fire group are powered down and would require a delay to power up when switching fire groups (this would occur before power priorities are utilized to determine order of dropping power)
in regards to an exploration ship... there's nothing about how this game does exploration that would need anything specialized other than jump range, which is already ludicrously high on many ships. You'd need to add more environmental and other obstacles to exploration that dont exist in the game to make having something called an "exploration ship" matter.