Source for that? I did some looking around but I've read nothing at all about anti-popes or investiture in CK3, good or bad, which doesn't mean they are precluded at game launch.
It comes from AsaTJ ("patch notes guy"), with a post on Reddit where he got some info about the game:
BONUS ROUND (Stuff that didn't make it into the article):
* There will be five unique graphics sets for clothes at launch: Western (European), Middle Eastern, Sub-Saharan, Indian, and Steppe. Everyone else uses whatever is the closest match. In terms of physical appearance, the new DNA system can represent all ethnicities, so we probably won't see face packs again. No era-specific clothing at launch.
* Clothing is partly based on rank. A Western Count and a Western Duke might wear a similar style clothing, but one wears linen and one wears silk and you will be able to see that difference.
* No more static event pictures. Events will feature the actual character models posed against some kind of background, and they can have props like knives, crucifixes, etc. Currently they don't animate to actually interact like getting into a fight.
* Tutorial is described as "Stellaris-like", and they've improved the ways the game can give you suggestions on what you want to be doing. More approachable, but not dumbed down.
* Custom religions you found can have Holy Orders. Not ready to talk much about that.
* The tech system is more tied to characters than it was in CK2, but not ready to talk about it yet.
* Councilor jobs like Steward are now an "office" that is placed on the map instead of a person, so you don't have to re-assign it when the councilor dies. The office itself can even still keep working without a holder, just at a very reduced effectiveness.
* The new Doctrines and Tenets are being used to represent more historically accurate versions of real heresies like Catharism. The AI will found these, and they are weighted to appear at the place and time they did historically. The AI will stick to founding historical heresies and won't abuse the system to create random weird ones. That's the player's job.
* Zoroastrians can still have incest, naturally, and you can reform any religion to allow it now.
* Historical events like the Mongol Invasion are in. Dynamic epidemics from Reaper's Due are not in, as they didn't feel that feature worked very well. No word on how the plague will be handled.
* Characters still get sick and are treated by Court Physicians.
* Provinces now have Development, which is like civilization value in Imperator. Tribes don't care about it but feudals get more taxes from it.
* Revolt Risk has been replaced by Control, which is going to work a bit differently.
* If your heir when you die is an old guy who has already invested all of his perks, you can respec his lifestyle tree once if it sucks.
* Splendour is like your Dynasty XP. It's used to buy Legacies, which are kind of like national ideas in EU4 and stay with your dynasty forever. One of these lets you increase the chances of inheriting congenital traits, if you want to create a dynasty of stong genius ubermensch. It's not realistic but it is a playstyle they want to support.
* Foreigners don't care about Dread, only your own vassals.
* Fleets are now handled like CK1. You just pay money to turn into boats. Naval combat is a possibility in the future. Henrik thinks it would be cool, especially for the Mediterranean.
* Vikings can still sail up rivers.
* There is a big dragon hanging out in the Terra Incognita on the Eastern edge of the map and it looks like they've left plenty of room to add China in the future. They wouldn't say anything about it. No Chinese Emperor interactions at launch.
* No plans for a CK3 to EU4 converter.
* You only need to siege the fortified holdings to occupy an entire county. Castles are automatically fortified, but cities and churches are not unless you have built walls in them.
* Factions are back. Peasants can now found factions. One example given was that Norwegian peasants living under a Danish king can found a self-rule faction, and Norwegian culture nobles will join them. Like a combination of a CK2 faction and a peasant revolt, very powerful.
* Henrik is not interested in non-dynastic play (Holy Orders, etc). Playable mercenaries are a possibility, being landless and using your armies to make money. Adoption is also a potential mechanic. Neither one will be in at launch.
* Much more events that deal with interpersonal drama and people important to the player, like family/friends/rivals.
* Events can look back at how the relationship between two characters has developed over many years and generate content for them dynamically.
* Poetry generator that will actually make your poetry better or worse based on character skill.
* Double the number of content designers working on CK3 as CK2 had at its height.
* Direct vassals will always matter. So the previous comment about Barons not being important doesn't necessarily apply if you're a Count.
* No crazy fantasy events (immortality, Satanism, child of destiny) at launch. Undecided if they will be added later, but if they will, there will definitely be game rules to turn them off. CK3 should feel more historical compared to CK2. This was a goal.
* There will be special mechanics for Crusades but they're not talking about that yet.
* Playing pagans feels "significantly different" from CK2.
* You can reform from tribal to feudal.
* Control is more of a short-term thing and Development is more long-term. For example, Control in a province is reduced when it changes owners but recovers quickly.
* Religions have degrees of relation. Abrahamic > Christian > Catholic.
* Eastern Religions are still more tolerant of heresies.
* Ecumenism: Catholics/Orthodox/Coptic don't treat each other as heresies for purposes of CBs and stuff. There are steps of tolerance. It's not just "True Faith, Heretic, or Heathen".
* Converting foreign rulers with your chaplain will not be in at launch.
* Investiture system and antipopes will not be in at launch.
* When you found a new religion, some vassals and some provinces will convert. Based on things like opinion modifier and traits (Zealous/Cynical)
* Terrain type has an effect on Development in provinces, but climate currently does not.
EDIT: No inventory system at launch.
