a) I don't know internals well enough to decipher the proposal. Is allocation on the stack a performance optimization? If so has any metering been done to see whether it actually impacts performance? If you would like opinions from me and perhaps others perhaps you could say a few more words about what the safety issue is? When is the JVM stack cleared?
b) If you are going to be doing thinking about compiler architecture I would very much like to see some thought going into debuggability. My current impression is that the trend is downward with more and more cases of not even being able to see function call arguments in slime. For example, at this point in ABCL's development, I think having a compiler option that pays performance for the ability to view local variables in the debugger should be an increasing priority. Other's mileage may vary, but in my case, where the bulk of time is spent in java libraries of various sorts, improving lisp performance is a distinctly lower priority than improving developer productivity by making it easier to debug.
2ยข, Alan