If ring signature is better than coinjoin, adapt ring signature to dash. Is this possible ?
The ring signature vs coinjoin debate was over months ago. Ring signatures won, bigly.
Dash was supposed to have them, but Duffield decided to betray everyone who bought Darkcoin for its privacy/anonymity/darkness.
Ring signatures are going to be implemented in V2. I will begin development immediately after I opensource V1.
...and it never happened.

Same thing with the silently broken promise to implement Masternode blinding. Duffield just pretended like he never mentioned doing it.
The problem is that Dash can't innovate. Heck, it can't even keep up with new Bitcoin features like RBF and segwit.
And here come the cult apologists to Duffsplain why it's OK for Dear Leader to make promises and never keep them....
Ring signatures would be hard to apply to dash or there would be other reason for him. This is reader's choice.
Because of tech difference and superiority, monero became major altcoin.
Your Supervise about dash make strain dash-dev-team.