MIRA has been mentioned for a long time as the RocksDB feature and it's definitely a key feature.
Something that helps improve programmer's accessibility to data . for now , accessibility to data on the blockchain is loosely on the apis which does not make access structured and comprehensive enough.
MIRA will make it more structured and comprehensive without a need for developers to index and store data on their own.
The new feature MIRA is going to solve the infrastructure cost and it can make the ecosystem more decentralized now from developer's point of view and the cost of running a node is going to reduce significantly. The outsiders will also have an impression that it is cost effective, faster and more decentralized as well with MIRA( Multi Index RocksDB Adapter ) in place.
With the recent announcement by steemit Inc, it has done with its first level implementation and they are currently working on debugging and testing. With steemit Inc struggling lately to run the nodes and especially the infrastructure cost, MIRA will be the stepping stone to lower the infrastructure cost. With MIRA, blockchain nodes can now store all necessary data on disk in a modern database.
The most interesting thing is that now the entry level to run a steem blockchain node will be lowered now with MIRA and that's great new for mass adoption as any common man can afford to run a node now, that means it will be more decentralized now in other words. It will also be more cost effective for developers and exchanges now than the past. So in a nutshell it is really a great news going in to 2019.
Thank you and Have a great day.