Scalar fields – make a universe? At first and with certainty, in fiction, yes you can. Beyond there, you might require a little more effort.
They have value in fiction and in spurning the imagination to continue exploring, so I wouldn’t trash any theory, so long as its kept in its proper place of “that of a fictional universe”. Who knows? Perhaps some discoveries in the fictional universe will end up relating to our own and even if they do not, other discoveries may come of it such as new technologies.
So, follow your bliss! If you have a scalar theory that you love, follow it.
Allow me to give a pragmatic example of the usefulness of a scalar field universe theory:
Interactive immersive fiction in the form of video games. For programming they can be very useful.