Messaging: In addition to basic SMS messaging (insecure, but there for convenience), the phone will utilize E2E via OMEMO on launch, with Matrix-based communication as a backup. Eventually E2E in Matrix will be supported. Messaging is already solved, though it will require people creating accounts to use via the Matrix protocol, so yes, you do have to combat the network effect.
Additionally, as a Social Purpose Company, Purism is legally obligated to serve social good over taking bigger profits, so they would be sued out of existence the moment they sold anything to Facebook. Not gonna happen.
Given that everything is open-source, anyone can take a look and figure out how to run and modify things. Purism doesn’t need to support it for it to continue existing in some form. GNOME exists as a separate organization, KDE exists as a separate organization, the Linux Foundation exists as a separate organization. There are many communities with interests in this phone.
The phone uses ARM. Linux already exists on ARM. They already have the devkit (and you can see videos of software running on the devkit being posted daily now at https://social.librem.one/@purism ). Purism does hope to switch to RISC-V once it becomes more viable.
The devkit has a functioning camera. Linux has a plethora of photo apps. The devkit has functional texting and functional phone calls. Linux already supports contacts, calendars, notes, browsers, and mail. This all already works on devkit (or can be made to work with relatively little effort at this point). Maps is bigger challenge, but Open Street Map exists, and open source navigation apps exist and work which utilize Open Street Map. Traffic data is missing, though, which is admittedly a shame.
Anything that runs on Linux will run on this phone, barring performance concerns and potential display issues by not fitting the mobile screen. But GTK and Qt have libraries which will auto-adapt windows to work on mobile screens, so existing Linux programs just need to pull in those libraries (if they are GTK-based or Qt-based) to work reasonably well on the mobile form factor.
Hardware is what is it - you can’t get top of the line specs at a reasonable price without being as large as Apple, Samsung, or the others. If you have many millions or billions to throw Purism’s way, I’m sure they’ll take it to leverage some better hardware.
It seems to me that most of your issues are actually solved. The hardware will suffice, even if it doesn’t have everything you want.
Maybe it is overhyped as a security phone and maybe not, but there’s no other phone that will give you this level of control over your hardware and software, and there’s currently no other viable Linux phone. Yes, I know things like the Pinephone have popped up since the Librem 5 was announced, but from what I can tell, Purism has made significant contributions upstream to enable Linux phones in general. Plus, I for one strongly appreciate their commitment to open-source as much as possible. I would buy this phone just for being a Linux phone, even if it didn’t have the killswitches. Do I think I will be able to fully replace my phone with it on day 1? No, or at least not without compromising the fully FLOSS nature of it. But this one needs to succeed for there to even be future versions that get better.