@Johan, can Paradox do for HoI4 the nice thing one of the users suggested for EU .I think it was for EU, can't remember his name or find the topic, but it went something like this:
After some time (let's say two years) the DLC is merged with vanilla game, giving two important benefits:
1. After few years after release it is not required to spend 100 EUR to get full game experience.
2. It allows you, devs, to improve or build upon mechanics implemented in the DLC without the need to release said mechanic in yet another DLC. (like in last CK devdiary Doomdark wishes that Retinues were part of the main game or like you actually had to put National focuses in two EU DLCs so government ranks would work as designed). Also the problem of balancing new changes with superset of DLCs is reduced.
That of course relates only to gameplay DLCs, not cosmetic ones like unit or music packs.
The most important argument against it was iirc that why should some people get for free stuff that other have to pay for, but I think that would no longer be the case if you state when DLC is released that after two years it would be merged with core game. People will know what they are paying for and would have a choice (pay and play for two years, or don't pay and wait two years).