I need to echo Mike's comments. What is the differentiator between Plyxon and PL/SQL Developer? So far, based on the screenshots, I don't see a difference. Even the look-and-feel is the same.
At the moment, the landscape for Oracle development is frankly fragmented and frustrating. Oracle SQL Developer provides strong support for the latest/greatest Oracle features, beyond what PL/SQL Developer provides. On the other hand, its overall setup is very weak. Oracle has recently released an extension for VS Code that is very nice but feature-deficient. At the moment, I am bouncing around between Oracle SQL Developer and PL/SQL Developer, but I have to say neither meets 100% of my needs. As a simple example, I am in the process of migrating my on-prem database to AWS RDS, but I am struggling with simple things like exporting objects without including the low-level details like which buffer cache is used or which tablespace is used to store data. PL/SQL Developer does a great job with this...but does not recognize automatic partitions, nor does it recognize compression settings. As a result, I have to do a lot of global search/replaces, which is painful and time consuming.
I really really hope Plyxon can fill this niche: support for mainline DDL (which includes features that have been in Oracle since 11g), support for debugging and procedure development, and support for DevOps tasks like moving data from instance to instance. If it's delivered as a VS Code extension, that would be a bonus, but I understand if you prefer not to yoke yourself to a specific IDE, even if it is the flavor du jour.