I know fredding this will be difficult ,but you will not see those two battle in first main campaign.
Icanus will be appearing in the last "combat" mission and engaging one or two ships for plot purposes ,and will take part in final "parade" mission.
Eclipse will get attacked while under construction and take part in parade (I'm thinking of nonlineral campaign ,so if you fail to protect it things will get much worse and you will not see it on parade).
Both are flagships ,so you will almost certainly see them if I will make you visit home sector of either faction in second campaign (with is especially likely with Eclipse).
I will certainly learn a lot when trying to get either ship moving.
Also i see a problem with hyperspacing ,especially i want to use $use Newtonian dampening in AI profile.
It will make it go on insane speed and certainly will be hard to make look decent.
Imagine this ship slowly emerging from the hyperspace and forcing all ships to cease fire (I will not say many more because it's a huge spoiler. The point is i want them to feel a bit like FS1 Shivans. I can only say it will explain a lot after blasting troublemakers).
Slow entering is my idea to compensate Newtonian dampening ,and when i tested it on Orion Refit it looked awesome ,and forced the ship to go mere65 mps ,which make it stand in place I wanted him.
On Icanus speed still will be huge (65mps will make it warp through 5 minutes) but it will be using LRBBeams
so i hope it will not make a problem (Rift Cannon will be scripted anyway).
As for flying above Eclipse it will be more like a planetary mission.
I want to use carriers extensively so there will be one point where bombers appear (although you will better stay away from it because it will be a heavy carrier with escort).
Also speed of fighters will increase to around 400mps (still lower than modern fighters ,but with 800mps and corresponding side speeds it starts to act like TMP getting very hard to control witout proper interface).
If there will ever be bugless build with TMP features and INF ship limits i will make fully Newtonian version.
Still it will be almost certainly very hard to FRED so superships will appear in last part of campaign.