The variety of units / nations / theatres etc. that are covered is immense, so I suspect that you would be hard pressed to find a situation that is not covered somewhere amongst all the material that has been published over the years. As far as I'm aware, there is still material being published for it even now.
MMP is publishing 4-6 products a year, including bonus packs, reprints of major modules with significant updates, starter kit expansion packs, and historical and campaign modules. There are also several third party publishers (TPPs) producing modules.
A couple of years ago MMP released a pocket version of the rules. You'd have to have a large pocket for it, but it was still a nice soft-bound book that would easily fit in a backpack. It was a big step forward from the 3-ring binder rulebook. Earlier this year MMP finally released an electronic version of the rulebook. It's a PDF, but there are links throughout. Now I can carry my rulebook around on my iPad.
There has always been a dedicated group playing ASL on VASL, but when COVID hit last year, it exploded. The face-to-face tournaments are starting again. Our club held our small tournament earlier this month, and there are two more larger tournaments coming up next weekend - one in Atlanta and one in New Hampshire.
I'd say that ASL has had a minor revival in the past 5 years. Preorder numbers of 600-800 are usually reached within a month. Still, the fanbase is aging, and most players are probably over 50. Another trend has ben the rise of the starter kit (SK). It was originally intended as a programmed approach to learning the game (first infantry, then guns, then armored vehicles), but it has grown into a pretty legitimate game system on its own. MMP has published close to 100 scenarios, and SK now covers the Pacific theater. It's 80 percent of the fun of the full game but with only 50 percent of the rules (or something like that).
Are there any modules for periods other than WWII? I don't know but no doubt someone can enlighten me on that.
Forgotten War is a major module set in the Korean War. I have it, but have not had a chance to play it yet. I don't hear much talk about it, so I'm not sure how much it is getting played.
Above is a photo from the end of the game I played last week. I was the defending Russians, and my opponent had the attacking Germans. The scenario was set in Smolensk in July 1941. The Germans started at the top and had to wrest control of three large buildings, including the one you can see with both German and Russian units. The initial German force was strong, with numerous quality troops, and MGs. The defending Russians were weak conscripts, but they were fanatic so they were a little more robust, and they were in stone buildings. On turn 3 the Russians received some good reinforcements, so the trick with playing the Russians was to trade casualties to buy time and hold off the Germans until the reinforcements can come in and fortify the last large building. In particular, the Germans couldn't get too far down the map and set up fire lanes with their MGs.
The Germans started off with some bad luck, breaking their heavy MG, and losing a 5:1 close combat. I managed to get 6 Russian squads and a medium MG into the last building, so I thought I had built an impenetrable fortress, but then in a string of low firepower attacks, he managed to break 5 out of the 6 squads by rolling low over and over. The dice giveth, and the dice taketh. He also took out a light MG I had positioned to cover any advance he would have to make to enter the building. In the end, he managed to get two squads into the building, but I had one unbroken squad left in the building, which denied him control, and the Russians held on to win.