Huge fan of the old-school DD1, and there's a lot of reiteration from the community as to why they loved it in the first place. So, I'm just going to be selfish and post what I'd like to see personally anyways:
1. Map-Specific Loots (you guys could even try rotating the specific loot-drops of maps between different periods of time to promote perfecting every map, idk). Bring back the old style of rare rewards for the fun grind that we were so addicted to. This also helps culture a player-driven economy with items of rarity and whatnot, which was a big part of the original.
2. No delays for loots. While I am unaware of the current state of DD2, when I first played, I received a pet egg as a reward. The incubation time took 6 hours to a day or so if I recall correctly. While you guys have said that there will be no microtransactions, I still wouldn't want to see this sort of waiting system implemented anyway into DD:A. Everything in DD1 was pretty much instantaneous, as a looter genre should be.
3. Endless Modes, various other game modes, + Leaderboards. Stimulate competition. Stimulate the desire to push players' strategies, stats, and builds to the limit, and for casual players, it's still fun trying to last as long as you could for that little robot pet.
4. Seamless multiplayer. Having the freedom to join in with friends in maps without any sort of restrictions and joining randoms through the matchmaking UI was simple, pure fun back in DD1.
5. End-Game. Legitimate, hard-core endgame. Something to work for. I do not, and I repeat DO NOT mean scaling stats on enemies on the same maps over and over again, although the challenge is nice to push for the never-ending cycle of increasing gear tiers, but I digress.. When I mention end-game, I mean exclusive-to-the-end-for-the-end content. Something enticing (a few crazy maps with a certain theme, maybe an interesting boss(es) with challenging mechanics never experienced before, a really crazy/challenging "exclusive to select end-game/new maps" game mode, I don't really know myself); to motivate players to grind out their best strategies and builds and attempt to win or not even win, but just to last even a bit longer than others. (Perhaps you guys could create this content as an outro to the story you guys are working on for the whole of DD:A, or an intro/teaser as to what DD3 would be about, but I'm not a dev, so this is merely my fantasies and rambling)
DD1 is a looter game, and it's fantastic. When you add more elements to it that make the looting even more purposeful for challenging content without certain delays that we experienced in DD2, it becomes a gem people don't mind sinking hundreds, if not thousands of hours into.
Also, unrelated to Maps (sorry), but y'all are on an aggressive development schedule as you've said yourselves. While I am excited for updates and for this product to be out ASAP, I also want to play a polished DD game. I would rather play a polished version of the game that came out later than expected, than a ragtag shamble of graphics that was pushed out just to meet a deadline. (Remember what happened to Diablo 3 at first release, as well as the recent negative backlash on the newer release, Anthem). The game will grow if it has a positive launch. I highly doubt there will be growth for this old gem of a title if launch is less than decent, especially with the unfortunate track record of previous DD titles.
With that being said, you guys have my full support, and I have high hopes with the amount of passion I'm sensing through your PR. Good luck Chromatic, keep up the work!