-snip-
RKVs would be fun as a citadel building. Near lightspeed slug cannon, expensive and maybe huge energy upkeep while it's charging, maybe one use, long travel time as the slug is sublight, but nearly impossible to stop and tombs planets from multiple systems away. Add some brinksmanship to your multiplayer games, do you really want to start a war when it might mean MAD?
Do you *really* want to wait several years for the impactor to reach even the closest of targets? Perhaps better would be some form of superluminal weapon that fires shells from system border to system border as if using a jump drive with extended range, and has a very fast in-system velocity. You
can shoot it down if (
if) you've got fleets close enough to intercept.... but you'd better be packing lasers and some good FC or you're not going to burn off enough of the massive shell before your planet gets turned into 1/2 planet and 1/2 brand-new ring system.
Or, you know, just make it nigh-uninterceptable save by planetary defenses (and even then only high-power laser type weapons or the occasional lucky kinetic strike) and have it truly be a bad idea to attack anyone who's got these things (make FEs extremely difficult to just steamroll even in the later stages of the game, anyone? You might just need to sacrifice something to the superweapon before you manage to finally defeat them...)
But yeah, besides the details I think it would be hilarious and awesome to be able to construct something like that.