I think it's fair that Steam users get something good out of it, the Workshop could potentially be even remotely as good as RTB, with or without saves
What's the point of it being on Steam then aside from more purchases? You can put Blockland on Steam just by adding a non-Steam game and bam, you have the in game overlay
RTB doesn't come default with Blockland, and there's still many that don't know about RTB and how useful it is, the Steam version of Blockland could have a button right on the main menu for opening the Workshop where you can subscribe/unsubscribe to various things
It just doesn't feel right having the game on Steam and NOT having a single difference from the non-Steam version
The Workshop can just be an alternative to RTB, there's no harm in having both anyway (other than being redundant)