Season 6 is going to happen because they already promised it, and going back on their word now after a year of radio silence would be a bad look. After that though I fully expect active development on DRG to end. I also don't expect S6 to be of any real substance.

One of the reasons why they decided to make Rogue Core a separate game rather than an expansion is because DRG is very old and its codebase makes it difficult to add new content, especially on the scale of Rogue Core. Frankly, given how buggy the game is and all its performance deficits, I believe them.

They've already proven they can't work on two games at once when they tried to develop DRG and RC simultaneously, so why would they keep indefinitely supporting a 9+ year old game they clearly want to move on from? The writing is all over the wall.