There's a high possibility for Cardano to take over the top spot only if ETH will remain slow and expensive.
Things are not that worse in ETH like it used to be, the fees have dropped down but it is still expensive but still people use them and as long as there are developers and investors invested in ETH it will rally.
Its actually hard to tell because many are still using ETH network despite of the issues with the fees and the slower network. Honestly, I don't want to choose because I believe both of them have a bright future so better to hold both than to choose on which one is better, time can tell but for now ETH is still the top choice of many.
Since it is a purely speculative market, you never know when some of the crazy investors start investing heavily in Cardano and once that happens the price would rally.