Do you think you would be able to have a profitable bot?
What would we need for our bots to be profitable?
Bots could easily become profitable as soon as people start filling asks and bids. Having a market maker bot would basically enable you to set your spreads i.e. Buy at feed -x, Sell at feed +x. In the example of BitUSD:BitBTC these spreads would move in relation to the current Bitcoin exchange rate. This would be trivial to implement and in already liquid markets the risk would be relatively low in comparison to BTS markets (as price manipulation would be minimised across external exchanges)
If a given market becomes more and more liquid, do the bots keep their profitablity?
(I'm sorry I am pretty new to trading bots)
Yes and no - competition increases and so spreads tighten but volume also increases.
For example, I could write a bot that buys at 1% below actual price and sells at 1% above but somebody else runs one that only looks for 0.5%.
Ultimately, when this starts to happen bots begin to become more intelligent to compete.