I would really like to play one. Just imagine: a colony planet 200 ly away sends a report that it is on the verge of a thermonuclear civil war. You dispatch a sleeper ship of marines that will reach the star system in 600 years. When they arrive, 800 years have passed since the war and the colonists have an industrial society and refuse to pay taxes for 800 years. Your marines can't waste 400 more years on talking with you, so they nuke it from orbit, strip-mine the cities for metals and reseed the colony. Meanwhile, another colony has overtaken you on the tech tree and seceded 100 years ago...
Indifference is Bliss
What's so funny? I'm totally serious. It's the only way to communicate how ****ing big the distances in outer space are.
Have you read The Forever War by Joe W. Haldeman ? It addresses some of those issues.
I've read A Deepness in the Sky.
On the plus side, that sounds realistic, sort of. On the minus side, it doesn't sound fun. What do you do while waiting for the ship to arrive at the other colony, click "next turn" 800 times? And you have no control over what happens on the other colony, and don't even find out what happened until 200 years later (1000 after the initial message)? What's the point of "owning" the other colony, anyway (in a 4x game), if it takes so long to get stuff to and from there?
"Your Vega III industrial colony produced 300 units of ore and shipped them to you 50 years ago. You should be getting them in another 150 years. Message also reports Vega III under attack by ruthless space monsters, so this is the last of the good stuff, sorry."
You spend these 800 beaming orders to other colonies, managing your space fleets and planning your production and research orders. Of course, 1 turn should not equal 1 year, and the game should fast forward through boring times.
So, you only control research and production on one colony, and send orders out to the others which will be long-obsolete by the time they get them? Sorry, but this is sounding like an area where verisimilitude is in direct opposition to fun.
If you want to wait around forever and a day you can mod FTL out of Sword of the Stars. One of the races already has its primary means of travel as STL(they build gates later so you'd have to mod those out).
As for FTL coms,sensors and whatnot there isn't a good way to replace human decision making just yet, see Moo3 to get your fill of that.