I've done one all dungeons run, I felt it worked out easier (not necessarily faster with practice) for the Ultimate Evil run I did, it's a nice change. Something like All bosses would make the basement boss more relevant across the board though!
If we will be using the Dev discord can we link that, otherwise we could just set up our own for speedruns. My thoughts on future ending would be start a fresh file, obtain Necronomicon, go do future ending at it's most basic, timing works the same then and you still play the game to show as much off as possible. You could do it from a previous save but I think it loses a big part of it's value as a speedrun that way, but that's just feelings not a logical argument.
Will there be a category for the future ending, or is that falling under good any%, obviously it's a bit curious as it requires having all other endings first, but I definitely think it's unique enough to be it's own thing, especially with having to get the Necronomicon before you can get to it. Also is there an existing discord? I personally find discord a little easier to discuss things like categories and rules etc.