Worst thing that can happen if you count as playoffs: Someone scores more than 19 playoff goals, breaks the record for most in a single run. Who cares? There'll be an asterisk here as it's in 5 rounds vs 4 rounds (similarly, when NHL went from 2 to 4 rounds, no one started comparing raw stats of the 4 round era to 2 round era, right?). So no real harm. Will be an amazing performance, and people will be smart enough to recognize 5 vs 4 rounds.
But regular season....i don't think that's fair, because not everyone gets a chance to finish regular season.
Who wins the Rocket? Ovi, Pastrnak or Matthews? Matthews may have 7 games as a 'play-in' and score a bunch of goals. How many games will Pastrnak and Ovi have in round robin, 2-3? You could similarly put up an asterisk on a season, but putting an asterisk on a whole season when it was ~90% done seems like a shame.
Also - 'not counting at all' is dumb. These will be highly competitive situations - I think they should count. So - playoffs.