I'm really not as worried about our defense as everyone seems to be, for a couple reasons.
First, we've got genuinely good defensive prospects. Hronek is scoring at a 40ish point pace as a rookie, and Cholowski's right around 30 points pace as a rookie. Pretty impressive. McIsaac battled through injury this season, made Canada's WJC team early (and was a big part of it), and is scoring in line with the top defensive prospects of his draft year while playing a solid defensive game. See no reason why he can't project as a top four defenseman. Maybe Gustav Lindstrom does too, though it's a bit more murky. And then our ranks are loaded with depth guys. And that's all within our own organization.
Second, the idea of "you need a elite #1 defenseman" is overblown anyway because nobody seems sure what that means. Quite a few people around here were positive that John Carlson wasn't a "elite defenseman" on the Caps way to the Cup last year. Vegas certainly didn't have one. Pittsburgh has one in Letang, but their most recent Cup was won without him. Unlike centers, where I really believe you need a game breaking talent, I'm less sure you need a star on defense as I'm sure you need two really good pairs. I think we've got the makings of that.
Finally, it's nothing you can't fix in free agency. While I've loathed the idea of trading for Trouba for years, nabbing him in free agency a year from now probably changes the entire complexion of the blueline. Same with Josi, Tanev, Muzzin, Spurgeon, Vatanen, Faulk, Barrie. All are FA's next year. Many of them will get re-signed, but some won't. That's what free agency is best for, filling in gaps.
I would be really really loathe to reach too far on a defenseman in this year's draft given all the offensive talent that will be available. I still think that our center depth is our biggest organizational weakness at the most important position.