4+4 is a really bad idea. #4 defensemen are replaceable defensemen you can find in UFA and trades every year for a reasonable cost, and by the time expansion rolls around, our #4/5 defensemen should probably be Liljegren and Sandin anyways (both exempt). Kapanen, Johnsson, Kerfoot or whoever we decide to protect with those extra three spots are a lot more valuable than any #4 defenseman in this league.
We should not need another top 4 defenseman besides Rielly, Muzzin and Dermott (or whoever we trade him to get). Holl will be the one who is exposed and it is not a big deal if we lose him.
Protect as many guys as possible and do not worry about trading away assets to protect an extra guy either. If anything, just trade away a roster player for assets.
Know what else is easily replaceable? Forwards 7-8-9. Mikheyev is exempt, we can game the system with a UFA Hyman. Say we can sign (or trade a KK/AJ) for a solid borderline Muzzin class D with term, and Dermott emerges as a protection worthy young top 4 dman. Why weaken the roster by trading away hard to get things that help the team now and in the future when we can just let Seattle have a forward we can replace?
Option 1- Add a top 4 D, plan to protect 4 IF Dermott emerges (bold = exposed)
Next year
Top 9 F: Tavares/Matthews/Marner/Nylander/Hyman/
Kapanen/Mikheyev/
Kerfoot/
Engvall
Top 5 D: Rielly/Muzzin/xxx/Dermott/
Holl
Post expansion = Same less one of KK/Kerfoot/Engvall/Holl
Option 2 - Go lean, ensure that we only have 3 D worth protecting
Next year
Top 9F - Tavares/Matthews/Marner/Nylander/Hyman/Kapanen/Mikheyev/Kerfoot/Engvall
Top 5D- Rielly/Muzzin/Dermott/Holl/Sandin
Post expansion- same less Holl
Sure potentially losing Kapanen is slightly more painful in vacuum than Holl, but 4 worthy defenders + Holl before and a guaranteed 4 after lets us be a better team in both years.
That Kap/Kerfoot/ Johnsson are "a lot more valuable than any 4 in the league" is flat out crazy. If that was reality one would not be a Leaf today. And more importantly, if they were and that trade could be made for a better than 4 defender we would do it, and then the question becomes Dermott vs. one of the remaining two.
Of course, if Dermott doesn't emerge the point becomes moot and we let them choose between two of the defenders, after being a better team in 20-21 than if we jettisoned a player to position for expansion