Well, we already have systems with 32 electrodes, and we are looking at alternative to increase this by several orders of magnitude. I hope we have something next year.
If you talk about learning to play doom, I would say it is unrealistic at this point and still a topic of research, the purpose of the neuroplatform is precisely to find reliable ways to train neurons to perform a specific task.
There a Python interface. The API enables to send stimulations, measure action potentials and deliver dopamine in real-time. There are 2 videos that explains this in more details on: https://finalspark.com/neuroplatform/
I am not sure lack of immune system is our main concern so far at FinalSpark. I believe it has more to do with the side effects of physical contacts of neurons (and glial cells) with not fully biocompatible materials like the electrodes.