HACS is such a major part of Home Assistant. While I understand separation to keep some QC of integrations, I feel we can achieve this by different methods. Following is personal preference/proposal.
HACS - On/off option
To install HACS, I hope we have simple On/Off in UI may be under integration page. When turning it on, it warns user, this is not officially supported. When user agrees, it gives step by step instruction for GitHub account creation and token generation.
Unified Integration List/Store
Once HACS are installed/turned on, all integrations show up on single integration search page but with couple flags.
All HACS integrations has its own label e.g. just HACS icon on the right upper corner or perhaps change color of integration title to HACS background.
When installing ANY new HACS integration, user will be prompted THIS IS unofficial integration. Are you sure you want to proceed?