I mean, this is probably going to devalue a lot of your Modern cards, but your original printings are going to be worth more because they're more rarer and also "pimp."
Personally, I'm overjoyed they're doing this because they needed a way to make the format more "open" to players without destroying Standard formats by reprinting Dark Confidant and Goyf.
Also I was a big fan of the Terminator joke in the video about Tarmogoyf. re: He's a future-shifted pre-print from a set he's a reprint in.
The biggest thing this does is decrease the insane value of some commons/uncommons, and also possibly some rares that are being rereleased as Uncommons.
I would invest heavily in MM.
I don't really like the Tarmogoyf's new art. For one he
looks way too big compared to the original art where he was maybe 12 to 16 feet tall. Also I just don't like it.
As for the rarities, I wouldn't be surprised to see the rare staples being all mythic, this is a money grab set afterall.
Also am I the only one expecting to see a
Doubling Season reprint?
Doubling Season is a Commander card so I don't think it'd work out the way you think.
I don't think the Mythic rarity will be used the way you think. I expect a reprint of Thoughtseize, but it'd be the literal opposite of what they said Mythics would be used for if they upgraded its rarity. I fully expect, for example, Urborg to be reprinted at Mythic, as well as stuff like... idk, Chord of Calling? Kiki-Jiki? that sort of stuff -- big splashy mythic kaboom effects (as vanilla as Goyf is, it's still a potential 8/9 for 2 mana).