Is there any possible way to create dataflow with R without using R plugin (writing the script directly in DOMO just like sql)? If no, is there any plan to develop that?
Currently I don't know of another way. There is an idea that has been "Assigned Pending Review" to add the ability to use R within ETL transforms: https://dojo.domo.com/t5/Ideas-Exchange/Dataflow-Ability-to-write-R-or-Python-code-within-a-ETL-Dataflow/idc-p/25719#M5025
Might be worth upvoting to throw some more support behind it.
Hopefully we'll find out more at Domopalooza next month (that will be one of the topics I'm hoping to find out about as well).
If you are headed to Domopalooza; you may hear some very encouraging news on this front. There are definitely plans for this in the works.