A treadmill of better versions of the same craft you already have isn't really any more interesting.

Thinking about the tank/sniper/lancer type craft, it's actually a pretty good idea for a cruiser. Although I don't use heavy cruisers enough to tell what they're good at in the normal game, the long ranged cruiser could work as a counter to heavy cruisers in a mod at least. Where HCs would be able to dominate most of the weaker frigates and cruisers, except carriers, but particularly able to tank long range frigates and flak, the long ranged cruiser would be able to fire a powerful shot from outside the HC's reach, doing considerable damage before its mitigation goes up. It would also be able to function like that for a first strike weapon since it could do it's greatest damage before ships' mitigation started rising, but since it would be anti-whatever HCs armor is, results would vary. It's ability would probably fire some disabling or splash damage warhead like the artillery cruiser idea.

Since it's basically a gun with an engine it wouldnt have that much armor or shields, so frigates could take it out in groups or strike craft, and it wouldn't fire that quickly either, the idea being to hit while mitigation is low and then prevent it going higher. While it could probably take out cap ships in groups, the slower firing and lesser amount due to cost and fleet supply would keep their numbers low. It'd probably be decent against carriers while still dying to their SC.

Actually, Lancers and Destroyers are capital ideas...

And HC's take out large targets but get holes punched in them by smaller ones.  That is where I came up with the idea of Defense Cruisers.  It took about a month of going back and forth between Rezo, myself and a few others, but we eventually decided that a DC would be a wonderful compliment to the HC.  Basically, its partner.  HC takes out caps/cruisers, DC takes out frigates/SC.

Once again read my mod (it is after all devoted solely to adding new ships)...  If not, I'll explain it here in a brief summary.

Lancers have very good linear acceleration and have the highest linear speed of any capital.  They are giant tubes, so it makes sense.  However, they also turn incredibly slowly.  This makes them easy pickings for the fast and agile Destroyers.  Lancers also have 80% of their firepower forward facing with much of it focusing fire, thus making them cap slayers once they get lined up.  The level 6 ability is the activation of the axial cannon which is a death sentence as it either does insane damage, or in the case of the Vasari, bypasses shields/mitigation and heads straight for the hull, knocking out any hope an enemy would have of saving the ship.

Destroyers are faster and more nimble than lancers.  Though they cannot outrun a lancer, they can out-maneuver one.  By simply staying away from its bow, Destroyers can quickly take down lancers with their vast port and starboard weapon banks.  Their damage is enough to take down lancers, but not enough for a battleship.  Battleships will always win a 1-on-1 with a destroyer due to their abilities to counter and absorb vast amounts of damage.  The Kol is a rock.  The Radiance returns your damage by absorbing damage as AM, and the Kortul just counters everything you throw at it.

This creates a combat triangle out of the combat oriented caps.  Sure, others like the Marza can do battle, but only the ones I just listed are truly meant for direct combat.

Also, it should be mentioned that the artillery frigate is a separate suggestion from the lancer idea...