In video you have spoken about readiness for academic use. One really missing feature is still breakout rooms. This is not only for academic use, but also any use, where group work is needed.
Yet another huge missing (killer) feature is conversation recording and later publishing for participants. Appropriate feature request exist since year 2018. At least audio, video but also text would be appreciated. As it is custom storage, the space or usage bandwidth should not be issues. Would be appreciated, if there could be choosed, whether to record text, audio, video or all of these. Also flexible publishing would be appreciated, e.g. how long, permissions over shared videofile, etc.
You’ve spoken also about editing messages feature (also killer feature) and you claimed about missing real use case. Well, this feature request has been reported since 2019, has clear explanation about that feature. It is really annoying to delete-paste all the time about messages instead of just fixing them. Especially, when later try to fix - it will really mess up whole conversation, when I delete a message and insert it again into end of conversation. It really matters for organizations and is real obstacle of adopting Nextcloud, as also described in this comment and I can confirm it.
Yet there is one big missing feature, called delta-sync, block-level sync, Dropbox calls it also binary diff. Please look also Dropbox’s magic pocket. This is especially crucial in case of large files, internet connection bandwidth limit. Appropriate feature request about delta-sync has been created already in 2016. I would say, it is second missing killer feature after Talk missing message editing feature, that preventing of adopting Nextcloud in larger organizations and, or in case of need to sync larger files and, or using mobile internet with limited bandwidth for connectivity.
Really annoying are missing apps compatibility in case of Nextcloud 23.x and still I cannot upgrade. You mentioned, that you won’t pre-advertise, but I would say, that you actually did this. Only clean install is possible with v23. As soon as I try to upgrade, there are lots of incompatible apps, e.g. SSO / SAML authentication, which is mandatory for organizations with central user management. But there were also many other apps, that seem to be updated slowly.