Warning: These views are highly oppinated and might have some slightly incorrect facts. My experience with typescript was about 2 weeks in Node and a week in angular2.
TypeScript is implementing their own take on JavaScript. Some of the things they are writing will likely never make it in an official ES* spec either.
Technologies that have competing spec / community driven development have a history of failing; take: Flash, SilverLight, CoffeeScript, the list goes on. If you have a large code base, picking TypeScript is something your going to be living with for a long time. I can take a bet in 3 years JavaScript will still be around without a doubt.
Its also worth noting that they have built some things like module system and as soon as the spec came out they ditched it and started using that. Have fun updating!
