Yes, that is correct. And it is also worth mentioning that the incorporation of those mechanics (estates aside but their integration to the base game was rather iffy at the start) was seen a step in the right direction (at least in this forum). But it took how many years for that to happen? Also, it took Johan getting into the team for them to decide that it was a bad idea trying to maintain two code bases for government types & reforms.
I'll give them credit that that was a step on the right direction but it also begs the question of why not incorporate other crucial features locked behind half a decade old or even the entire DLCs. For example, why not roll American Dream, Res Publica, Wealth of Nation and Conquest of Paradise into the game?
American Dream is a very small, old and hidden DLC that marginally improves USA and nothing more. They can't touch USA because the country has an entire DLC dedicated to it, even though said DLC is below today's standards.
Res Publica marginally makes republic better and is also extremely old. I do wonder if one of the reason that they don't touch factions and barely address the republic issue is because of this DLC (it adds events, dictatorship and factions).
Than we have Wealth of Nations which is kind of useless nowadays because its selling point, TC, is also available for those who own Dharma.
Lastly, CoP, the first DLC released and one which had some great ideas that also show how PDXs development priorities changed with time. What this DLC do is add a MP sink for NA tribes and some unique buildings. These additions are cool in theory but America in general is very buggy and haven't seen any meaningful improvement or bug fix since El Dorado came out. Rolling the mechanics from this DLC into the base game would certainly help with some of the bugs associated with it.
I'd also add that rolling SLCs into the base game would attract new blood as a consequence of the general price of admission going down and the store front getting de-cluttered (is this even a word) as a consequence of there being less stuff to buy. I know there is no hard evidence one way or another but I think we can agree that a long standing issue with PDX is the amount of stuff you can buy for each of their games.