Yep, it's flying under everyone's radar right now too. In my experience Graviton 2 instances are ~20% faster and 30% _cheaper_ than the best x86 instances for typical web workloads (transform some templates, talk to a DB, do IO bound network work, etc.). It's an amazing way for nimble little SaaS startups to pluck away customers from giants by offering much cheaper prices. The little guys that build up ARM expertise are going to be great exits and pickups for the larger fish in the ecosystem too (because if your platform is an old thing with a lot of technical debt, moving it to ARM is not trivial and the expertise to do it is in wild demand).

If you're working on online services and NOT looking at or using ARM servers right now--you are in big trouble and already too late to the game.

What are the challenges with porting to ARM, besides third party code which doesn't support it?

I only know about unaligned reads and the weaker memory model, but both of them are already undefined behaviour in C/C++/Rust.