I still think the most direct comp for Chychrun is Hanifin. Hanifin was 27yo and signed an extension with a team he was traded to instead of testing UFA. His three years before signing he had 133 points in 242 games and averaged 22:31 a night. Vegas has treated him like a strong 2D where he was playing the second most minutes of their defenders but for the most part was on his own pair with Hague away from Peitrangelo and Theodore.
Chychrun over the past three years is at 95 in 177 (a ppg of .53 slightly behind Hanifins .55ppg) and an almost identical 22:38 ATOI. The games played and his inability to stay completely healthy is fairly significant for me going forward, and IMO basically nullifies the fact that Chychrun will hit UFA a year earlier than Hanifin. OTT's defense was a mess last year and Chychrun never had a consistent partner or a real defined role, something that should be better but not clearly fixed in WSH.
If the TOI, points, and role stay the same as they have the past couple of years there's your extension -- 8x$7.35M. You can probably give a $0.5M buffer on either side for whatever reasons. Maybe he loves DC and Carbery and is willing to take a bit less, maybe Ekblad and Theodore sign extensions early and he's the only good UFA and his market heats up.
To really break above that to me, he's going to have to demonstrate he can be a legit 1D and given how our defense is currently constructed I see very little room for him to get that opportunity. Carlson will (rightfully) get PP1 time over him and unless they put him on the right halfwall as a lefty shooter I don't see a path to huge powerplay minutes that would boost his point totals. With the Roy signing too they now have enough depth where they won't need to load him and Carlson on a top pair that plays 25 minutes a night. I think it would take an injury to Carlson or Chychrun really finding a new level as the clear driver of an elite second pair with Roy.
If he does that and all of the sudden can get $8M+, that's a good problem to have! If he plays at around the same level as he has the past couple of years, I see a clear path to a reasonable extension with some extremely clear recent comps. If he's worse, you can wait and see how the market plays out. If for whatever reason he walks at the end of the year it's not like you gave up anything to get him anyways.