I think you are asking the wrong audience. We can't speak for Oracle. This is the public-facing space for JDev & ADF. All you get here are personal views fo other users.
Here is my personal view or answers to your questions:
1) Yes, 188.8.131.52 is a stable version. A 'smooth' update can't be guaranteed. It depends on the code you have written. This code we don't know (neither does Oracle). You have to migrate to 184.108.40.206 and see what you get. I migrated projects without any problem, but other projects and problems which we needed to address. For the groovy problems, you should file an SR.
2) no comment other than that you should ask this over at https://cloudcustomerconnect.oracle.com/pages/home
3) no. We had this conversation over and over again already.
Oracle does provide WebLogic 220.127.116.11 version in the cloud. See - Oracle WebLogic Server for Oracle Cloud Infrastructure
As for your groovy issue - did you report this to Oracle Support?
There are some groovy related fixes in the latest patch we released for JDev/ADF 18.104.22.168 - so get that one from Oracle Support.
As for the status of Oracle ADF and it's future - Oracle ADF A Status Update