I'm not sure if this is worth anything to you, but there's still an active community on reddit at /r/spelunky, and there's a an active discord channel too. Most members there still play daily and we upload runs to mossranking. I expect you might already be a memeber, but if you're not you should definitely check it out

Oh! It somehow didn't occur to me that there is a Spelunky discord. I''ll probably join it sometime; thanks.
Regarding Reddit, I don't think it has the feeling of community that this place did, being a single subforum and all. I do lurk there for the content, though. There are some fun highlights.
To stay on topic, I'll say a few more things I'm hoping for in the sequel.
1 ) Returning characters. Even if they're all really old or something, it would be utterly heartbreaking to not see
Little Suzie make a return.
2 ) Spelunkers with different abilities. In Spelunky Classic, you could play as the Tunnel Man, who had an indestructible mattock instead of a whip. On a similar note, it would be nice to have the Damsel as an unlockable character again.
3 ) Challenge rooms. They were a neato feature in Classic. 'Nuff said.
4 ) Online multiplayer. On LAN netplay between PS4 and PS Vita, the players had independent screens, which worked perfectly. Additionally, having independent screens could make large deathmatch maps a possibility.
5 ) Larger levels? It's a matter of personal preference, but I think levels should be 1.5-2x larger to support more exploration. Multiple paths through a given level would be a good add-on to this.
6 ) Remove the ghosting mechanic. It does add an additional risk to high score runs, but the tediousness far outweighs it. I rarely attempt the Daily Challenge because I know I don't stand a chance against the players who wait an extra minute after digging out all the gems in the level, then lure the lumbering ghost through the gems scattered all over. That's the second of the two flaws in the game design I mentioned in my first post.
7 ) A level editor.
8 ) Mod support in some form. Whether it's an engine open to gameplay modifications (à la Spelunky Classic) or some huge official resource like Skyrim's Creation Kit, it is without a doubt that mods increase a games longevity. People were playing Spelunky Classic even after HD came out because of fresh-dope mods such as Tastes Like Spelunky.