Actually alien 3 and 4 could be made 4k too because cgi is so limited in alien 3. Alien 2 has no cgi. Alien 4 cgi would need to be done by professionals who would have to use the cgi models from original resurrection and then make them higher resolution and have them walk all the same way etc, Would really need top professionals. There wasnt much cgi in resurrection, the swimming scene and some other but they basically could be done too.