Dash is based on an outdated fork that is several years behind the current Bitcoin 14.x release.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.
$ dash-cli getpeerinfo
[
{
"id": 159937,
"addr": "[2100:efc5:1f::1f:bee5]:9999",
"addrlocal": "[2602:41da:2:d8df::1]:42952",
"services": "0000000000000005",
"relaytxes": true,
"lastsend": 1489360272,
"lastrecv": 1489360278,
"bytessent": 227688307,
"bytesrecv": 147711601,
"conntime": 1489087170,
"timeoffset": -1,
"pingtime": 0.117579,
"minping": 0.117387,
"version": 70206,
"subver": "/Dash Core:0.12.1.3/",
"inbound": false,
"startingheight": 633580,
"banscore": 0,
"synced_headers": 635317,
"synced_blocks": 635317,
"inflight": [
],
"whitelisted": false
},