About Tablet and TOH: theoretically, if tablet was designed like 2x phone (two cameras at the back, ability to connect two TOHs to the tablet's back), it would be very interesting. It would provide advantage of stereoscopic vision (if anybody cared to use it), large display (tablet, after all, has to be large), ability for two people to interact (be it for a chess game, or document-writing on an airplane), and other phabulous (play of words: fabulous and phablet) functionality.

About Vsenn...
It's not unusual to offer user-replace-able battery, though I do not see any advances in battery technology over time (Polarcell is a bit stronger because of size-volume, not quality-contents, imho).
It's possible to replace camera in Nokia N900 and such, but requires extreme care and caution, due to fragility - and, it's difficult to find something compatible and of higher quality-specifications.
RAM is easily replace-able in laptops-desktops - such a feature would be welcome in phones.
Processor replace-ability? Sounds like stuff of legends, with all the compatibility issues: you cannot put OMAP5 into hole from OMAP3.

Nice movement, but it will take a lot of work to make the phone future-proof through upgrade-ability.

I am not trying for Ara-like "design anything from any pieces"; rather, I am aiming for "choose whatever screen(s) and keyboard(s) you like", while core (processor, RAM, camera, sensors) remains the same. I just consider removal of screen as next logical step (see below), with two TOHs at the same time being a really nice feature.

If people can make a screen-TOH, what's the point of having a screen inside Jolla Phone? If people can make a keyboard-TOH, what's the point of having a keyboard inside Jolla Phone? [wait, Jolla Phone does not have a keyboard] If people can make a Toggles-Buttons-TOH, what's the point of having hardware buttons inside Jolla Phone? [wait, Jolla Phone doesn't have hardware buttons]

And yes, having the "vulnerable-malicious-power-hungry" components plug-gable in-and-out would help. Even if you would have to design custom-shaped USB pluggies, to make them fit the shape of the phone better: most people would just leave them inside, while the random paranoid people would be glad to have the option to take them out, or replace them with a different piece of hardware.

Best wishes. Thank you.