Yes. PetSets are intended to be step one of "some things need to be stable and replaceable at the same time". So that unit can then be composed into apps (i.e. Zookeeper + Kafka might be a PetSet for ZK and multiple scale groups for Kafka). basically trying to boil the problem space down into "what do cluster aware software need to be safe", like protection from split brain and predictable ordering.
There is likely to be more needed (on top or around) because we need to also solve problems for highly available "leaders" and active/passive setups. Think of what something like pacemaker does to ensure you can run two Linux systems in an HA fashion, and then map the necessary parts to Kube (fencing, ip failover, cloning, failure detection). Still a lot of hard problems to solve - PetSets are the first building block.
There is likely to be more needed (on top or around) because we need to also solve problems for highly available "leaders" and active/passive setups. Think of what something like pacemaker does to ensure you can run two Linux systems in an HA fashion, and then map the necessary parts to Kube (fencing, ip failover, cloning, failure detection). Still a lot of hard problems to solve - PetSets are the first building block.