Paradox have announced a historical grand strategy expansion blowout-o-rama for June 14th, when they'll launch the Third Rome 'immersion pack' for Europa Universalis IV [official site] and the Death or Dishonor 'country pack' for Hearts of Iron IV. Yup, both on the very same day. Paradox had a similar plan in April, releasing Europa Universalis and Stellaris expansions on the same day, so I guess they're confident a grand strategy double-header is not as odd an idea as it might seem. For players who do want both of 'em, Paradox will offer a small discount. It's a war-o-rama.
First, Death or Dishonor. Though it does introduce a few new features, it's not a full-size expansion, instead one of the class of add-ons focused on making specific countries more unique. Paradox explain:
"Death or Dishonor introduces new National Focus trees and gameplay options for the countries caught between the Nazi and Soviet war machines - Hungary, Romania, Czechoslovakia, and Yugoslavia. In addition, Death or Dishonor adds new diplomatic and puppet interactions, new music and gameplay art, and additional national interactions to change the course of history."
Here, check out this recent Paradox livestream showing them paying as Yugoslavia under DoD:
As for Third Rome, it's the first "immersion pack" for EU4, which is a similar-ish idea of focusing on specific areas of the world. Your blurb:
"Third Rome expands the governmental, military, and diplomatic opportunities for the Russian empire. The pack includes new ranks of Russian governments that give Tsars the power to claim states, powerful streltsy mercenary units that excel in combat at the cost of the empire’s stability, and new interactions with the Orthodox Patriarchate. These changes give Russian players more ways to maintain control over their sprawling territory using a mix of military might, political touch, and religious conviction."
And your developer livestream:
The expansions will cost £7.99/$9.99 apiece or Paradox will sell them together with a 10% discount for £14.38. June 14th is the big day.