[tomsem]

Everyone has their ideas about why Amazon changed to using MTP. I do not think there is any one reason.

First: it is not noticeably slower than USB mass storage, at least comparing file transfer times and how long it takes calibre (or MTP client/system file utility) to get directory listing, comparing Paperwhite 11th/gen 'PW5' to Scribe, both of which have USB-C interface. If anything, at least on macOS, it is faster for file transfers. MTP 'mounts' (or whatever MTP equivalent is) much faster as well.

It is probably a good guess that all future Kindle models will also use MTP.

They probably intended Scribe to have it when it shipped, but like several other features, it wasn't ready. I don't think it will be applied retroactively to previous Kindles, there are too many customers who would be impacted. At this point most people with Scribes never had USB storage at all.

Fire tablets also use MTP. So one benefit is that they share common way of connecting to a computer. It's very transparent on Windows (probably 75% share?), where MTP client is built in to Explorer (thanks to the extinct Zune). It doesn't interfere with calibre either (except for thumbnails not currently getting copied for side-loaded books).

Then there's no issues with disconnecting cable during file transfer (we can debate whether there are any with USB mass storage, but both Windows and macOS complain if you do not Eject properly).

Finally there have been rumors that Amazon wants to update 'Kindle OS', perhaps with some flavor of Fire OS/Android (I have come to think this is the main reason for the change). This might let them share code with Kindle app, make it easier to update the reading app independently from the rest of the system. Switching to MTP smoothes the path to doing so.

And yes, this would probably mean Download for USB transfer would remain convenient path for DRM removal only if you had a legacy device registered to your account. It is only in that sense that it is about tightening DRM. It's more about streamlining development going forward, having convergence in development and testing tools, and making it easier to find people with the skills to work on it.

Currently, everything that USB mass storage lets you get at is equally accessible via MPT (and with latter none of it is 'hidden').

Harder to jailbreak, maybe. But not an issue for Fire tablets which are routinely jail broken. Not my area of expertise. But I doubt Amazon cares.

It's also less flexible to automate file transfers: no command line access with usual commands (ls/dir, cp/copy, mkdir, chdir, chmod/attrib, etc.).

On Windows, you can automate Explorer with PowerShell (from what I've read: have yet to investigate); on macOS I've managed to install a set of command line tools that comprise a thin wrapper on MTP library (brew install libmtp), but those tools in turn need some shell scripts or some other wrapper to make things simpler.

But for example, there's no cross-platform Python library for MTP (apart from what Kovid has done for calibre, which is tailored for calibre). Someone more experienced and knowledgeable than I could probably covert that in a few days to an official Python package that would be available from PyPi, etc. And could be used with Android devices.

As for Scribe vs. Elipsa for manga, I am Switzerland.