Hey our interest and background sounds pretty similar! I too have been looking for something fun to build that combines my two interest: ML and crypto.
My idea is to create a site that allows for people to run easy-to-deploy alt-coin trading bots that actually use machine learning. From my quick google, I found several crypto trading bots, but usually they are outdated, hard to deploy, works for bitcoin only, aren't free (e.g. Haas). Others that are open-sourced employ technical analysis, which in my opinion is not much better than reading tea leaves -- particularly when we're trying to automate the process and leave human judgement out of it. No proper pattern recognition is being done here.
From chatting with traders, it surprised me that many of them aren't even aware of basic ML concepts like how to fit a regression model, performing model selection, how to prevent overfitting etc. So what I thought is useful is a website that let people deposit their funds, select a few bots pre-trained on selected altcoins against bitcoin (e.g. a litecoin bot, a monero bot etc). The user then set their prior belief on whether the market is moving up or down, then he can run a test session before depositing funds and running the real thing. What we need is a model-based approach to doing this kind of thing, something a bit more principled like this latent source model, but implemented and scaled to work with real data in real time. Or perhaps a simple gaussian process regression will do, or maybe some of those NN that work well with time series data, I dunno ..
Additionally what could useful here is not just giving a prediction on whether the market is going up or down but also to update the posterior probability on the prediction, so the user can change his prior and adjust the bot accordingly -- all from the web interface. Basically the goal is to make automated alt-coin trading as simple as possible. I have only started to think about this in the past few days, but haven't really coded anything yet. Probably will start soon.