When a fan asked Magic head designer Mark Rosewater about how Mangara's ability contradicts what Rosewater thought about white's "intentional downside", here's what he said on his Blogatog: 

I’ve come to realize that I needed to reframe how I thought of white. Card draw is too fundamental to the game to cut out of a color.

We’re still going to keep it fifth in card drawing, but we’re working to figure out how to make card draw organically white in a way that doesn’t undercut its philosophy or flavor

Many MTG fans have criticized white as being the most underpowered color in Magic due its lack of cards that could draw cards, so it makes sense that R&D are giving white more card draw power to help balance Magic's color pie. 

Magic designer Ari Nieh, a.k.a. the "White Council of Colors representiative", recently confirmed that Mangara's reactive draw ability is not the only white card draw experiment you will see in the next few years. 

When we looked at white card draw, we decided that any white card with "Your opponents can't do X" also allows the text "Whenever an opponent does X, draw a card".

This is not the only white card draw experiment you'll see over the next few years.#WotCStaff https://t.co/CC5XEeOxC8

— Ari Nieh (@SixthComma) June 4, 2020

Core Set 2021 is set to release on July 3 with Prerelease events scheduled from June 26 to July 2.

Related: MTG War of the Spark Trailer Wins Royal Television Society's Award For Animation & VFX