Another thing to consider is that some plugin authors are going to add new features for SU 2016 and forward. This has to do with the change in security.
Some unscrupulous individuals have been opening RBS files and taking code that doesn't belong to them. Trimble added a new encryption strategy to protect plugin authors IP. I'm pretty sure they realized their own sales potential over this.
At least old versions of SU will still work with old versions of the plugins (minus enhancements and bug fixes).