The KOReader forum, AND the Kobo forum are not really bad places to post your idea.
KOReader runs on multiple platforms and therefore interests more than just Kobo users. Not only that, but its plugin system does not even require a clone, or even a compile! Their devs might have tips if you have a specific question about the debug process. Not only that, but there already IS a wallabag plugin!
The Kobo forum is relevant because Pocket users could give insight into their use patterns. There is in fact no shortage of Read-it-Later options - I've run a Shiori server and client on my Clara HD, modded a KOReader routine to execute an html-to-epub converter, and others just use Calibre or desktop plugins to save as epub to the cloud, for examples. The devil is in the details of what people find convenient.
Some options out there:
https://github.com/go-shiori/shiori#readme
https://codeberg.org/bins/sako-plugin
* Oh yes, there is also rmkit (C++), a super cool platform that supports some Kobo and Remarkable devices and has room for a spiffy read-it-later app.
** Actually, there is a great Gemini protocol (Simplified web protocol, not the AI engine) KOReader client, so you could contribute to the http/html to gemini proxies that already exist and help the battle against web bloatware!