A few years ago I bought a Kobo device. Not sure what it's called. I fired it up and it immediately asked me to create an account, with no option to skip the process. I thought to myself "screw that" and plugged it in so I could flash something like okreader instead. KDE automatically recognized it as a storage device, so I decided to take a look.
Turned out that the root folder contained a sqlite database. I opened it up, looked at the schema and inserted a new user manually. It worked just fine. No problems since.
I have no idea if the new devices are any different but given the overall quality of the thing I wouldn't be surprised if they made it so trivial to bypass their online service integration on purpose.
They absolutely have left that door ajar on purpose. Presumably they calculate that by being the de facto go-to reader for the people who want to install their own software, they can both sell more devices and don't need to splash a lot of money up the security wall playing cat and mouse with motivated hardware hackers (who would become pretty motivated if they found there were no open platforms). It's not as if people who would install koreader would just roll over and start throwing money down on Kobo store books. They'd just never buy a Kobo at all.
I have a Clara HD and it's a fun little Linux device (no android nonsense, just a good old shell), Koreader is pretty great (a few rendering bugs aside) and I can even ssh into the thing _and_ pull files down from my computer with WebDAV though the koreader UI.
What do you mean by install their own software? What are people installing on their Kobos? I bought mine just because Kindle doesn't have ePub support[0]. Now I'm curious what else I could do with it.
[0]I know about Calibre. I'm not willing to jump through any hoops for ePubs. This should be basic functionality on any ereader.
The MobileRead forums[4] are quite active, you'll find a lot more there.
[0] https://github.com/koreader/koreader [1] https://www.willus.com/k2pdfopt/ [2] https://github.com/baskerville/plato [3] http://pbchess.vlasovsoft.net/en/ [4] https://www.mobileread.com/forums/forumdisplay.php?f=223