Strongly agree. Ironwood (https://github.com/ironwood-lang/ironwood) takes that to the limit by throwing away the JVM :) The static type is the tag, so nothing is tagged at runtime. Primitives are machine-width values, references are one pointer, and generics specialize in the closed world, so the language has no boxing at all.

> If it's not your first rodeo in compilers, IMHO just design your runtime primarly for register-passable values from day one, it might feel like premature optimization, but since the value model will permeate so much of the runtime, the knock-on effects once you do decide to fix it probably makes it worth to go with it from day 1.

Day one, definitely. Those were cheap to fix only because the value model never had to change.