It was a great luxury to have a player like Kos in the fourth line. The only thing that can keep him so low in the lineup is that he hasn't played that long. Otherwise, he should definitely be higher in the lineup, he is a very valuable player that every coach wants to have in the lineup.
Sikora is definitely a lock in the lineup, he played in Třinec with the men and quickly became a fan favorite. In a way, he's a similar type of player to Kos.
I don't know Vaculík, only from the highlights, but if he was as agile a skater as in those videos, the possible line of Kos, Sikora, Vaculík would without a doubt be the most skating line of any czech team that I remember.