I think, you are mixing whole lot of things together and it is difficult for me to understand what is the end goal.
For instance, do you actually need Excel or are you just trying to have a matrix with columns and rows? And what is the connection between DataTable and Excel? Do you want to have a DataTable widget that you want to interact with?
Why do you need Shiny? Are you planning to run analysis interactively? Is that just for yourself (so you can run it locally) or are you planning to give it someone else to interact with (so you need to upload your Shiny app somewhere else)?
In any case, saving and loading data in R can be done with, for example, saveRDS and readRDS. Then you can use resulting file and put it anywhere you like, including S3 as it was done with Datacamp example.