Would supporting some form of USB oled screen be useful?

You can display certain useful yunohost statistics like ipaddress and activity

Welcome mofo,

I would say working on that kind of support for external devices would be a tad out of scope for YunoHost. However, YunoHost being based on Debian, any device compatible with Debian would be compatible with YunoHost too. The supporting software should be lean and not try to take over parts of the system handled by YunoHost.