For subdomains of wmf cloud second-level domains, see T125589. For completely random second-level domain registration (like what this ticket is for), afaik there are no plans to support it.
If you do want to host oawiki.org on wmf cloud, tool labs / toolforge may not suffice due to a shared url proxy. Neither will normal vps projects due to a shared domain proxy (the proxy will not recognize Host: oawiki.org). You might have to get a floating external IP and register the domain to point to the floating IP, unless some magic outside my knowledge happens.