I think it's a really bad decision.
You are making it even more difficult to move forward. A lot of people have invested a lot in this game and spent more than $1000 on DLC, keeping The Sims 4 going even longer is going to force this community into an even larger sunk cost fallacy. It's incredibly unhealthy and the decision to end the support of The Sims 4 is going to be even more difficult to take.
You are oversaturating The Sims 4. Packs are going to feel even more similar than ever because we are stuck on the same platform which is bound by the same rules that were created in 2014.
You will constantly chase technical debt. The game is built on code from 2014, is constantly getting new updates, every single line of code that is being added with every new pack is going to have to be compatible with 50-100 DLC packs. Trying to keep up with every line of code is going to be incredibly difficult.
You are going to be left behind. Technology is moving forward, the video game market is incredibly competitive and are coming up with new ways to attract people and build communities, the sims community is going to be stuck in the past unless you want to play on a mobile phone.
People's saves are going to become too large. The game is going to have to cache and load over 300+ lots with sims, relationships, build/buy, potential cc, autonomy rules, pack rules, and who knows what else. This is going to result in a save that will be similar to a software program having a memory leak where it will just grow, and grow, and grow. Noticed how The Sims 4 is using a huge amount of RAM when playing your old save? That's why. And it's going to get even worse.
The game will be incredibly vulnerable to bugs. Remember when all sims started getting mean to each other? Or when shower/bathtub combos stopped working? That was because they missed one single line of code somewhere, having everything built on top of each other means that it's incredibly easy to make a single mistake which will make the whole thing fall over and cause bugs. And the developers at EA/Maxis moves on, people need to replace their roles, maybe they are not familiar with what they did back then, many people that built the sims4 could have moved on to another company.
Going for the mobile market means that you have to compete with them. You have to spend loads of development cost against a market that is not as nice as the PC/IOS market that you had with the sims4. The mobile market is incredibly competitive. The success of The Sims 4 comes from it having no competition, that will not be the case with Rene.