Since we can have {} almost anywhere as a new block scope which can then resolve to a value which, so that entire block can be used as an expression.

This lead to a potential issue with early exit?

For instance with the line:

foo(a, {
  if randBool() return;
  b
})

There is a potential situation where a is either consumed by foo, or nothing is done, because during the evaluation of the second argument the function returns. What then happens to a?

We need to be able to track floating values, so that in the event on an early return, these floating values are safely disposed.
This also must account for nesting, i.e.

bar(c, foo(...), d) // c and d should also be disposed of