Not trying to make a huge argument, but the Blues have decided that they don't really believe in an "all-in window". We've quietly rebuilt over the last couple of seasons with the main goal of making the playoffs every year forever (we're not a huge market and that's how we stay in the black). Our older forwards are already being replaced by quality prospects, and we've got a pretty decent young core. It's not as young as, say, Toronto or Winnipeg, but we never went full tank/rebuild so we don't have those knockout, top-10 blue chippers to base the team around (aside from Petro, who's 28 now).

And don't hate on Kyrou. Not his fault he was picked 35th, and it has nothing to do with him as a player. Same as when I hear people write off his OHL MVP because he was D+2... nothing he can do but play his best hockey wherever he is assigned. And he's starting the season with Schwartz and Schenn on our 2nd line. You won't have to call him a "2nd round pick prospect" much longer. (He's also a better skater than Liljegren, had to get that jab in)

That isn't wrong, defenders do take a bit longer before they hit their stride but they also take a lot more punishment than most forwards so they do tend to run into injury issues more once they are over 30 than forwards do.

For the sake of argument let's say Parayko stays at or near the level he is at now till he is 32. The following things are issues that need to be kept in mind.

1) He'll be FA at 29 (4 seasons from now) and if he's the top pair guy, how much money is he going to want and what kind of term?
2) When he is hitting FA, so is Rielly and Kadri, are we going to sign all 3 to big long term deal? Kadri I think will take a shorter term deal and possibly Rielly as well.
3) What kind of a player is he going to be moving into his 30's (there is a very real risk of drop off in those years)

Now what about Liljegren?

1) If he doesn't play 10 NHL games this season, his ELC will slide another year forward meaning he has another 3 years of ELC ahead of him
2) When Parayko is potentially declining, Liljegren is just entering his prime.
3) After his ELC, the team will have far more power in negotiations. (Considering they will have so much tied up with thier star forwards cheaper controllable high potential players are paramount.)

So if we are looking at this from a long term perspective, its not the wisest move.

Even you are correct that defencemen hit their prime at 28-32 (Look at the best defenceman over the past decade and most are in their mid 20's) then Parayko is hitting his prime when he hits FA. What kind of contract is that going to be? 8 years and 10 million? No chance I am paying him that kind of money. So he'll go test the market.

For me the age difference is the biggest sticking point, I think if you add a 1st round pick, then its a done deal but I am also 100% positive that ends the deal as well.

I won't disagree with anything you said here. Sounds all correct to me, nothing I wrote was meant as an indictment of Kyrou, its more that the overall trade creates long term issues that I wouldn't want to deal with. Most people post trades and think about what it does now and the next season but rarely do they think 3, 4, 5, 10 years down the road and in the salary cap world, you really should think that way.

Parayko has 4 years left on his contract. That's plenty of time to be in the winning zone and wont take away from Toronto's window. If I'm Toronto and this offer comes through, I'd be stupid to not take it.