Sounds like this move will make Reddit worse in every way possible, which is a pretty impressive feat IMO.

1. Most (or all?) 3rd party apps will disappear. You’ll miss out on all the cool features that actually made Reddit useable.
2. You’ll have to see the ads again if you use the default app.
3. Accessing your curated multireddits will be harder. Just try the default app and you’ll see what I mean.
4. The UI will be full of trash such as “news” and “discover new subs”.
5. Lots of users will be gone. There will be less quality conversation and quality posts. This means that you will find fewer things worth reading.
6. Regulating bot spam and other sorts of trash might (or will?) be harder and less efficient. You’ll be seeing more stuff you don’t want to see.

If all of this comes true, Reddit would earn the ”most hostile move towards your users in hopes of an easy cash grab” -award of the year.