An interesting package! I am going teach lavaan this semester. I will try it first and may introduce it to my student. I still think writing and running script is the most efficient work flow. However, a shiny-based interface may be good for learning and testing.
Bollen, K. A., Harden, J. J., Ray, S., & Zavisca, J. (2014). BIC and alternative Bayesian information criteria in the selection of structural equation models. Structural Equation Modeling: An Multidisciplinary Journal, 21, 1-19. doi:10.1080/10705511.2014.85669
A good feature! Some users like one single window with panes. Some users like multiple windows. Some users like being able to choose.
I like the interface of GIMP, in which you can switch between single and multiple window modes. I also like the interface of Blender, in which you can work in one window with panes, as in RStudio, or you can work in multiple windows, which can also have mroe than one pane each, just by creating new windows.
I hope RStudio can be more flexible. I don't like the the single window mode when working on a small screen notebook.