Team Hacksung, the group behind the CyanogenMod ports for earlier Galaxy devices has said the team will skip the Galaxy S 4. XpLoDWilD explains this decision in a post on xda-developers:
Nobody at team hacksung (the team behind galaxy s2, note, s3, note2, gtabs… official CM ports) plans to buy it, neither develop for it. There are two variants which will be a pain to maintain, the bugs we have on the s3 will probably be there on s4 too (camera), and we all know Samsung ability to release sources while staying in line with mainline. Yes qualcomm release sources, but exynos sources we had were far from actual galaxy products. I’m pretty sure the same will happen for this one.
That’s a uniform “no” from us.
Samsung may be friendly to the millions of consumers buying its devices, but its relationship with developers is not so amicable. According to reports from those working on mods for Samsung devices, the Korean company has not released updates it promised to deliver and has misrepresented some of its products. Because of this rift, consumers buying the Galaxy S4 must be content with the stock ROM and its various flavors as an official CyanogenMod port is out of the question at this point.