I'd agree that Haiku is a great system, is simple, easy to use, and agree with some of your points. On others, I digress.
Haiku already supports gcc5 + gcc2 as well as x64; try a Nightly with said support -- on that note, Haiku just doesn't "stay still" and can't afford to. I agree features will need frozen to reach R1 soon, but the team is very good and well aware of what they are doing. Haiku does have the default application set you're mentioning: MediaPlayer, WebPositive, ShowImage, etc. But if you're talking about a flagship or featured app like Lotus 1-2-3 in its day, it's true that Haiku needs one. I'd think it'd be up to the Depot... and not the main OS to satisfy that burden. As for Terminal, there's fun stuff in the Depot you can install if you add third-party depots in Repositories; if you're talking the default shell you're using (bash), then switch to zsh, etc. instead.
And... why Qt? I somewhat dislike Qt for varying reasons; particularly because of its history and because the APIs used by Haiku and also Gtk are better. I know Qt is widely used, it's good to have choice, etc. but if Haiku were to choose something for third-party app developers to quickly bind to and join, the best choice is clearly to target Web applications using HTML5, CSS, JS, etc. Maybe support Vala, Python, etc.
Also, why "ditch support for old hardware"? Debian already dropped 32-bit PowerPC and vintage i386 (still supports i586+), and several major Linux distros are beginning to relegate 32-bit editions to legacy use or the bin. Why? I like that my old computers can run Haiku OS; it's something that nothing else, (save for Minix, ReactOS, *BSD, or a smaller, random system) can do nowadays. It'd be a strength for Haiku to maintain support for older hardware, all while supporting SSDs, EFI, etc. as it is currently trying to do.
As for drivers, Haiku appears to prefer BSD (correct me if I am incorrect) because it is more compatible with Haiku's license and vision than Linux is. Kind of sad... because Linux is more widely known and supported -- but the logic makes sense. And I agree: there should be a group for maintaining and coding applications and for developing the core system (kernel, etc.).
But for all of my (probably worthless) ramblings, my opinion really doesn't count for much. I imagine another's will supersede this one with much better points and experience. I'm just another random Haiku user, and otherwise, a spunky app developer. Back when alpha 4 was being phased out, I tried to fork Haiku; the only thing left of my royal failing (which I think the FOSS world laughs over) is a flavor/distro now reduced to Poem's Vintage app image. But here's the reality about attempting such an effort for the uninitiated: one can't change the way the Haiku system truly works due to restrictions in the distro guidelines. If one could dump needing gcc2 support entirely, change the system layout, etc., and freely rebuild Haiku, I believe it could take on Mac OS. Insane as it appears, yes, I really believe Haiku could do that. I love Mac OS, but there needs to be a good alternative. Because I can't utilize Haiku for that purpose, I guess that's why I've switched to a Linux core and am trying to work on a Be-like environment (facade) instead.
That said, I still appreciate and like Haiku... and would softly say to have patience -- it will someday reach R1 and meet all your goals and those of the project. Right now, it's barely at beta stage. In the meantime, have you checked out the Glass Elevator concepts for after Release 1?