I don't think that for a serious project it will be hard to appear on coinmarketcup. This is the most important obligation after the commencement of work.
I'm not happy with the coinmarketcup platform, but for some reason many investors trust it, I think that every project should appear there.
It has nothing to do with being a serious project or not. As far as I know it depends on the number of exchanges you are listed on. And also on the trading volume threshold, which I can't exactly recall right now.
For listing coins on coinmarketcap daily trading volume must be from $ 100,000 for all pairs on all exchanges.
But there for the calculation applies a certain formula.