"There's a chance" is the operative word there. You could easily say the same thing about at least a half dozen other defenders, probably more. But Sergachev's upside is undeniable. He's got a great package of size, mobility, skill and assertiveness (at least offensively). But there are some major questions about his commitment in his own end, and as minimal as I think the "Russian factor" is, it's still a risk that North American-born players don't carry.
All that said, the sturdiest, most projectable thing in the Coyotes organization is OEL (as slick as Domi and Duclair looked this year, they'll still need to prove it wasn't a fluke), and Sergachev's playing style looks a lot like OEL's, namely his poise carrying the puck through the neutral zone and his ability and willingness to fire wristers on net from the blueline. In terms of complementing OEL, Sergachev is not the best option and would probably be used not just on a separate even strength pairing but on a separate powerplay unit, too. Definitely an exciting prospect, though.
Not exactly. Despite being a couple inches shorter than Turris, Jost already has 20-30 pounds on Turris when he was drafted. To say he's more physically developed is an understatement. Jost is also not quite the puck wizard that Turris was in the BCHL (and he lacks the gamebreaking shot that Turris had), but he's a very creative player in his own right and plays a more solid game overall. He could probably use a year in college and then a year in the AHL before making an NHL team (and for his own sake, hopefully in that order, unlike Turris's path). Because he'll be drafted out of the BCHL, he also has the option of going to the WHL for a year and then jumping to the AHL, unencumbered by the age restrictions players drafted from the CHL face.
I'd project him to actually be a slightly more productive NHL player than Turris has been so far, something in the 30-goal/40-assist range with effective two-way play. Could be a very effective wing, too.