One of the Dominaria cards that players are the most excited about is Mox Amber. Historically, any card with Mox in the name has sweeping impacts across multiple formats. The restriction on Mox Amber is interesting, but many players are excited about the challenge of finding the right shell. As far as Modern is concerned, KaosOfMind has found a pretty good place to start:

Historic Hatebears - Modern | KaosOfMind, 5-0 Modern League

• Creatures (32)
• 1 Restoration Angel
• 2 Brimaz, King of Oreskos
• 2 Thalia, Heretic Cathar
• 3 Thraben Inspector
• 4 Blade Splicer
• 4 Flickerwisp
• 4 Isamaru, Hound of Konda
• 4 Kytheon, Hero of Akros
• 4 Leonin Arbiter
• 4 Thalia, Guardian of Thraben

• Instants (4)
• 4 Path to Exile

• Artifacts (6)
• 2 Smuggler's Copter
• 4 Mox Amber

• Lands (18)
• 9 Plains
• 1 Eiganjo Castle
• 4 Ghost Quarter
• 4 Horizon Canopy

• Sideboard (15)
• 1 Blessed Alliance
• 3 Burrenton Forge-Tender
• 1 Declaration in Stone
• 1 Dismember
• 1 Grafdigger's Cage
• 1 Kataki, War's Wage
• 2 Leonin Relic-Warder
• 1 Linvala, Keeper of Silence
• 1 Ranger of Eos
• 2 Rest in Peace
• 1 Sunlance

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Isamaru, Hound of Konda and Kytheon, Hero of Akros are your one-drops, and any draw that starts with using Mox Amber to play both of these cards on the first turn is going to be difficult to beat. You also have Thalia, Guardian of Thraben on the second turn as well as Thalia, Heretic Cathar on the third turn to help you power up your Mox. On subsequent turns, you're less likely to be using Mox Amber to help you curve out, and more likely to be using it to let you leave up interaction like Path to Exile or Restoration Angel.

The upside of this Mox Amber build is that you have some explosive draws that are very difficult for opponents to beat. When the format is all about racing, Affinity has shown us just how powerful a Mox can be. The downside is that you can't effectively splash other colors for cards like Tidehollow Sculler and Fatal Push or Blood Moon and Lightning Bolt, as you need to have a critical mass of legends to even turn on your Mox Amber, and even if you do it's probably only going to be tapping for White mana.

All in all, this seems like a great home for the card. Hatebears was already a very reasonable deck. We've seen Mox Opal become a defining card for multiple archetypes in Modern over the years, and there's no reason to believe that Mox Amber won't do something similar.