Hi.
Yes, Dragonnet will support java 1.12.
Yes the thread is two years old, but the last release of dragonnet is one year old. (https://github.com/DragonetMC/DragonProxy/releases)
Dragonets idea is to bridge bedrock to java, to make a bedrcok client able to join a java server.
Since bedrock edition supports only minecraft for tablets, phones, consoles and the windows 10 app, and it is over a year old, it is more likely than not that you will not get your clients to connect to it, but you will be able to connect your bedrock server to the backend minecraft java server.
You may be in luck though, since it seems these folks may have started up development again:
They have no official release yet (after a year of development on existing codebase), but it seems they have snapshots and betas available.