If you mean a paid, consumer OS, you've got to keep in mind that they're essentially tied to a hardware product. The vast majority of your target market is not

If you mean a paid, consumer OS, you've got to keep in mind that they're essentially tied to a hardware product. The vast majority of your target market is not installing an alternative OS manually. You would need to either sell hardware with your OS or get hardware companies to package your OS over the existing options. With how mature the personal computer market is, this is a very big hurdle.