The 12.1 release notes say no future fixes for 11.1 and N-1, so I assume Avaya won't provide support for an 11.1 system, short of IPOSS hardware replacement and software entitlement. I'm not sure what the differences are between 12.0 and 12.1 short of a making a quick dot release for R12 so they could EOS R11. I haven't put any systems on 12.X yet and have almost finished getting the systems I work with to 11.1. I don't like putting systems on the GA release of any Avaya software since they whacked the field trials many years back.
IPOSS policy will continue as N-1 as it includes maintenance and configuration support if needed and provide upgrade entitlement to R12.0 There are no additional Service Packs planned for R11.1 following the GA of the IP Office 11.1.3. Service Pack 2 July 2024 all future fixes will only be delivered in R12 Service Packs