Call it educated speculation based on years of experience with similar decisions.
How big is the team? How many years of maintenance have you had on those projects? I remember C++ looked pretty awesome for a while. It was certainly great for one-man projects or small team. Then the problems started piling up. Thing is, C++ didn't have any good alternatives (maybe now we'll have Rust); Scala does.
Scala is not C++. Scala has much better features to keep complex pieces of code separated from the simple pieces. Also C++ design philosophy was totally different from that of Scala's - C++ values performance over everything else, while Scala's top priorities are correctness and type-safety.
Nope. C++ is almost a superset of C (there are a few minor differences, but most C programs are correct C++ programs).
Even the most basic Scala program is not a valid Java program. They are just two different languages targetting the same platform.
If making analogies, a much closer analogy would be to say Scala is to Java what D or Rust is to C++.
As of lots of baggage - can you elaborate? Only null comes to my mind and it is never an issue - it was left because Scala is practical. Sure, there are some limitations imposed by the target platform like lack of TCO, lack of efficient suport for tuples/value-types, or RTTI for generics being not powerful enough, but Java-the-language has nothing to do with it. The same limitations apply to Kotlin and Ceylon.
