I think I fall squarely within the second two categories: Simulationist & Constructionist. Those two sections in Capntastic's OP described how I see DF and currently enjoy playing DF almost perfectly.
About DF currently: In the current version of DF I find I enjoy Fortress mode the most; both in vanilla and with various selected types of mods. I love the challenge and the Fun of designing and building a Fortress, as well as imagining the stories going on behind the base mechanics of what occurs. I love reading LP's and I may try writing up one of my own... eventually.
Most of my thinking (modding, planning, idle thoughts, etc.) that are DF related are focused primarily on Fortress mode. Mods I dream up are generally ones that are Fortress-centric, either introducing new civilizations & critters to wrangle & manage, or as enemies to pop up and offer challenges. I really do love how much customization of the world experience is possible by tweaking world generation and the raws for creatures & entities and such. Loads of possibility here.
In brief, what appeals most (to me) about Fortress mode is the free and open nature it has; deciding on ones own goals and how to best achieve them within certain parameters.
At this time I am not that fond of Adventure mode. From what has been discussed and mentioned thus far in the upcoming update (Necromancers, Tombs, etc.) this aspect of the game will finally (to me at least) have more of a point of playing. Currently I see Adventure mode as simply a hack & slash survival & exploration game; just wandering about looking at different parts of the world... and trying not to die. Can be fun, but needs depth.
About the future of DF: I am very optimistic that both Fortress & Adventure modes will get a lot better over time. I see myself focusing mostly on Fortress mode, with forays into Adventure mode to explore & flesh out worlds more, or as methods to 'set up' sites or locales for use as Fortresses in the future. If a method ever exists to reture a Fortress, I could see doing the same the other way around as well.
While I like the idea of adding more structure to Fortress mode in some way (themed starts, etc.) I do hope that more open styles of play, like those that currently exist, will still be in DF in the future for Fortress mode. Given what I know of the upcoming updates, I feel that Fortress mode will get a lot more interesting and complex, something that I really look forward to. Adding more interesting elements into the simulation will only enhance the experience IMO.
In my opinion the 'future' of Dwarf Fortress really lies with the Simulationist & Constructionist styles of play. This type of gameplay is the bread and butter of the DF experience thus far, and I would like to see more of the same: More complexity, more options, more ways to develop and build upon the worlds that are generated and, most importantly of all, more development that adds to and enhances the Simulation experience and thus which also offers wonderful opportunities to build and develop things as well.