I've just completed an integration with Home Assistant for my OVMS module installed on my Nissan LEAF. I couldn't find any existing resources on doing this so I thought I'd write up a quick blog post that explains how to achieve it. It's pretty simple, but the OVMS API docs were a bit hard to make sense of, so hopefully having this documented somewhere is useful to others!
I even did a (questionably useful) integration with HomeKit through Home Assistantant. It will remain a bit janky though until Apple adds an EV type of entity to HomeKit.
Hope this helps someone!