The old .dll wouldn't work out of the box anyhow - if it would (and were that simple), I'd have already released a compatible version by now.
There have been some major changes that needed to be addressed, but as
@Diesmon said, the compatible version is now in internal testing.
However, as I stated many times before: as the 3.1.x client doesn't provide any new features the bot would use and the most recent 3.0.x version doesn't have any known security issues (that I'm aware of), I don't see a reason for rushing here. Upgrading to 3.1, especially on Linux (with all its various supported distributions), needs more libraries to be installed / other manual steps to be taken care of, which requires thorough testing / preparation, as it would otherwise lead to many new support requests and waste time I'd rather spend on other functionality.
It would've been nice, if you had at least read the other threads about that topic where I already said most of what I posted now...