*This is all my opinion, feel free to disagree*
I'm not one to argue with anyone on this board as most of the time I feel as though people have solid logic behind their opinion, even if I don't agree. But I think that a blue chip prospect should be defined that if their projection stays on course, they'll be a Top 4 Forward, Top 3 D, Starting Goalie. (For a Stanley Cup Playoff Team)
Most of the players you take in the Top 10 are on course to reach one of those 3 areas, therefore I'd classify them as blue chip.
Sergachev was a blue chip because his project at the time was a 50 point+ Offensive D, which would put him at a #3 at least.
Poehling wasn't a blue chip, because he was likely going to be your 5th, 6th or 7th best forward. Now he's improved to the point where I'd say his projection is now 4th, 5th,6th. (Still not truly a blue chip).
Kotkaniemi's current projection (IMO), has him as a Top 6 forward, something like the 2nd, 3rd or 4th best forward. That's Blue Chip
It isn't a matter of question marks, it's a matter of projection.
Elias Petterson has one major question mark (size), but as of now his projection is to be a top line player, hence he's a blue chip prospect.
Someone like Martin Kaut isn't a blue chip prospect, because he's likely going to be the 4th, 5th or 6th best player on your team. That's not a true blue chip. If his progression continues, he very well could be a blue chip this time next year, but as of now he's at the door looking in.
Blue chip certainly can be used subjectively, but I think the general consensus is that it's about projection, rather than being safe.
Also a side note: The Kotkaniemi poll won't solve the debate, because there are some people who think Kotkaniemi is the 8th-15th best prospect in the draft, so to them he's likely to be the 4th/5th/6th best player on a team... Which again isn't a true blue chip.