Generally, everything is possible. But at the beginning, it makes total sense to add those cryptocurrencies which have big demand and liquidity. Also, it's a lot easier to list Bitcoin clones when you already have Bitcoin implemented than listing something completely new.

Generally, I like the idea of having the decision making process based on votes. As a suggestion, maybe it makes sense to combine funding with the implementation of voting based features and listings? Because that way, implementations with high demand can be easily determined AND developers receive compensation for developing features. Keeps the incentive high for everyone.