Roadmaps: http://tracker.ardour.org/roadmap_page.php http://ardour.org/development/post3.0
MIDI: those Atari apps you're thinking of didn't do audio.
General utility: perhaps you need to talk to various people who do, in fact, use Ardour instead of ProTools. As for the comparison with Reaper - Reaper is a very impressive project, but if you try it for pro- usage rather than home-style recording, you will very rapidly discover quite a lot of basic issues that they have not addressed, but were being done correctly by Ardour 8 years ago. I look to Reaper for good ideas and impressive development speed, but they really are focused on the needs of a different type of market segment than I really pay the most attention to.
It is true that there is no single DAW that is to everyone's taste, and Ardour is probably a more "acquired" taste than many others. At this time, I would say that more or less no DAW can easily "replace" any of the others. You can't really replace ProTools with Nuendo either.
jsprinkles: we distribute binary copies of Ardour from ardour.org that run on any Linux distribution (just about - we discovered a wrinkle that interferes with this on a few platforms, and the next release(s) will correct this).
disclaimer: I am the lead author of Ardour.
I've kept up with Ardour progress over the past 6 years and it has consistently gone nowhere while the major players innovate continuously. The assertion that Ardour has a chance at competing with the professional packages is absurd given that they've been promising basic MIDI support for years now, a feature that was present in software packages on the Atari. Add to that the fact that the project doesn't even have a roadmap for future development and it all looks pretty grim.
My previous career was audio engineering, and I can't help but laugh when the FOSS crowd insist that Ardour and Audacity are capable of replacing the industry leading software packages.
I think you might see interest in the platform develop if there weren't dozens of distributions to worry about. The distributions hamper Linux development, because you have dozens of different variants to try on, all with different versions of things and different bugs. As another commenter said, I bet you could get something Pro Tools quality if there was a consistent Linux-based desktop, not four or five frontrunners all doing GNOME differently.