True Improv Hexcrawl

Sort of tying into the general theme of the wilderness tiles post, someone asked on a forum if there were any hexcrawl tools designed for truly last-minute world generation. What he's imagining: you start with just a local area, and as the adventurers explore, completely randomly generated hexes are generated only in the areas explored,,, but although the hex contents are  random, they aren't arbitrary; the terrain and ecosystem fits with adjacent hexes, and information gathered before entering a hex influences how a hex is stocked. And to emphasize the point: this is during play, without the game stalling while the GM generates the hex.

I've certainly tried something like that in some of the Last-Minute GM posts, but the techniques are still fragmentary, and designed more for quick prep a few minutes before play, instead of during play. Plus, there's those last couple of criteria: I didn't try to maintain real-world logic when generating adjacent terrains and biomes, and I didn't include rumor generation.

There are some near-matches that fail on one or two points. The world prep rules for Champions of ZED are geared more for pre-game prep, so they would be clunky if used during play. The same applies to the very detailed hexcrawl obstacle system described in the Judges Guild Ready Reference Sheets. There are some elements in a sandbox tool in Fight On! #3 that might be useful, but this, too, is more for prep than for use in play. The same applies to Kellri's Old School Encounter Tools.

I don't think there is a tool that matches all of the criteria. But what other hexcrawl tools are out there that might have a tiny piece of the puzzle?