There are been hundreds of attempts using a number of different ideas. The reason for C++ and not those alternatives is there is a lot of C++ code. If most of my code is C++ I don't gain anything from your new language as I spend most of my time maintaining old code. Even if I use your language for new code that means I constantly have to remember if I'm fixing a bug using C++ code rules or the new language rules. Some projects have successfully done this and eventually re-wrote everything. However others have not and the pain of a new language is a problem.
The other problems with that approach means C++ is everywhere.
I know that I can find a good compiler for C++ when I want to switch platforms. Will your new language support my new platform? Will your new language even exist? I've worked on a number of projects where the code was written in some language where the compiler vendor is out of business. This risk works against all new languages (some have overcome it, some have not).
With C++ I know if I need to hire more people I can hire experts to help out. If I choose your language do I have to pay my new employees to learn the language for the first few months? Learning my code (which is always hard no matter what the language) is already going to be a problem using something that nobody knows just makes it worse.
Will your language optimize well? C++ being everywhere means that compilers vendors have put a lot of effort into writing good optimizers. When performance matters C++ will often come in first because of this effort.
In other words it's the same network effects that weigh down any attempt at creating a new ecosystem. So if you're going to do that, you may as well start from scratch and do things better from the get-go.
I read the suggestion as being about a new syntax for the existing language C++. For that you'd need 'only' a transpiler (and syntax high-lighter in your favorite support tools), quite possibly written in a readily available language, perhaps even C++. That should address your concerns regarding availability on various platforms and optimization. Your other concerns of course stand.
I, for one, find different languages with similar appearance needlessly confusing. I what the experience with different syntaxes for the same language would be.
The other problems with that approach means C++ is everywhere.
I know that I can find a good compiler for C++ when I want to switch platforms. Will your new language support my new platform? Will your new language even exist? I've worked on a number of projects where the code was written in some language where the compiler vendor is out of business. This risk works against all new languages (some have overcome it, some have not).
With C++ I know if I need to hire more people I can hire experts to help out. If I choose your language do I have to pay my new employees to learn the language for the first few months? Learning my code (which is always hard no matter what the language) is already going to be a problem using something that nobody knows just makes it worse.
Will your language optimize well? C++ being everywhere means that compilers vendors have put a lot of effort into writing good optimizers. When performance matters C++ will often come in first because of this effort.