Dash is based on an outdated fork that is several years behind the current Bitcoin 14.x release.
Dash 12.1 is based on Bitcoin 12.1 codebase, released on 14 Apr 2016 - so 11 months ago, not "years".
Dash [...] has managed to break IPv6 functionality.
You can repeat it endlessly, it does not make it true: Dashs IPv6 capability is identical to that of Bitcoin 12.1.
If you are going to participate in a forum about software, you should be aware that software development time is measured in developer years, not calendar years.
Dash is 1000s of years behind the latest Bitcoin release and will never be able to catch up with hot new technology like RBF/CPFP, segwit, Lightning, etc.
Bitcoin had working IPv6 support in 2012. Cite:
https://bitcointalk.org/index.php?topic=81378.0Dash broke its inherited IPv6 support in v13. Cite:
https://github.com/dashpay/dash/pull/1065#issuecomment-252503008