Back in the early 90s, I was sharing drawings of starships with friends via snail-mail.
One of the concepts we speculated about was what it would be like to extend the lineage of the Starship Enterprise beyond the Enterprise-D, which was the latest one at that time. We wondered what extremely advanced starships of the 26th century and beyond would be like, say, the Enterprise-H or the Enterprise-R.
One idea circulated for the Enterprise-H was a massive city-ship, morphed from the old saucer 'n cigars design concept into something that looked almost like a gigantic multi-headed mushroom. IIRC, it has a crew of thousands.
I came up with a couple of similar ideas of my own. My concepts were called galaxyships, being that they were designed for intergalactic travel. My idea for a Galaxyship Enterprise-H took a couple of forms, one was a Federation-Klingon hybrid. The other had a shape similar to the Enterprise-D, but was many times larger and combined elements of Federation ships, Gommtu (TNG "Tin Man"), and the Borg. This gigantic Enterprise-R was supposed to be a living ship like "Tin Man", with a crew of many species including a resident Borg hive embedded in the ship.
Both my Klingonish Enterprise-H and my "alive" Enterprise-R were built to haul a fleet of smaller starships that would be carried along for the intergalactic journey. Once the Enterprise would arrive at its destination, millions of lightyears from its home port, it would "drop anchor" in some foreign galaxy and disperse its smaller starships to explore. The Borgified, living Enterprise-R had the additional advantage of something like the multi-vector mode of separation seen in VOY; the ship could split into four warp-capable "motherships", with each one proceeding to position itself in a different corner of the foreign galaxy being explored. Smaller starships inside each mothership would be dispersed from there.
I never got deep into propulsion, but I did vaguely assume these advanced galaxyships would explore the Universe using either some kind of transwarp conduit or fifth-power warp drive.
One of my friends envisioned a "cities in flight" concept, which I interpreted as being like a Super Star Destroyer or Death Star, but with a mixture of Starfleet, Borg and civilians/colonists on board.
