Ive already written a blog about environment strategy, and for some this is still valid, but since I have written it my opinion has changed.
Befor...
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the problem with the shared env approach is once you start using Dataverse as storage you end up with a huge amount of tables and possible security issues with regards to sensitive data in production which will be even more difficult to manage
Very true, and I would always scale out separate environments for large Dataverse projects. But in my experience the volume of solutions don't use Dataverse (your milage may vary). My version 1 was focused on Dataverse like you said and that is good for some, but I found its negatives out way the positives.
On similar thought process wrote about automation ALM