To me I hope the dekes don't slow you down, but rather that the faster you go the smaller chance to succeed.
Like we've seen in a few videos already, and the team have mentioned it; if your going on top speed your shots will likely miss target, and you'll lose the puck easy if engaged.
I hope the deking works in the same way.
If they are now introducing a whole new skating engine, and the whole "top end speed" thingy it'd be a shame if I was on a 1-on-1 breakaway, and trying to use my speed to get past the defender, deke, and my player automatically slows down.
No... I'd rather he kept the speed, but lost the puck due to not being able to control the deke at full speed.
If I wanted to, I could let go of the left stick to start gliding, getting in control and then start the deke.
That way I have an option, and the control is on me.