Question: Has GW come close to this in the subsequent years? If not, that would be a huge thing to add (for me) to the survey.
No, you can't scale from a skirmish game to an EPIC sized game with a single rules set. The closest is probably 5th edition which had support materials to do basically kill team scale, combat patrol (2-3 units), to normal games, all the way up to Apoc. If you want to run apoc, set as side a weekend or have multiple players on each side to help move everything lol. There is a fair amount of cross over in the rules sets though.
I know people have integrated kill team, combat patrols, standard matches AND BFG into their own campaign system, but BFG will use BFG rules. Some campaign start small and build up to an APOC game. So, you can certainly make things work.
5th had ALOT of additional books, not in the way that 7th and 8th did, they weren't needed to play the base game, they just gave you different ways to enjoy your collection.
Part way through 8th they release a separate "apoc" game, which let you play Apoc scale games in about the same time as a 40k game. It actually needed less dice than a 40k game lol. IT wasn't what people were expecting and they didn't really want this sort of version of the game, so it died out.
EPIC has continued to be supported by the community, for me, it suffers from a lot of the same problems 8th and 9th does with regards to movement vs weapon ranges, and just units being able to scratch tanks to destruction.
GW has basically taken on the video game model, where the game doesn't even have to be working correctly before its shipped (hello BF2042), because they can quickly pump out "patches", and just like video games those patches tend to break other things... 8th and 9th feel very much like you are play testing the game and just when it gets to a decent place, they drop a new version and make all the same "mistakes" again.
In all honesty, GW need to pull it all back to bare bones, so play testing can be effective. Write everyone's codexes at the same time, release the lot of them (you could still stagger them if you really wanted to) and then use white dwarf to release new stuff as beta rules getting them ready for the next edition, like they did with warhammer fantasy 6th era. As the community keep trying to tell GW, most or the old armies actually have all the tools they need, we don't need new units, we are move than happy with new sculpts that are not space marines