Can I say
He is yet to be a murderer.
to mean the he is not a murderer, but very soon he will be one?
I think this could be construed to mean something different, depending on context. It could actually be a rejection of the notion that the person mentioned is or will be a murderer.
This means that whatever bad things he has done, he has stopped short of murder. It is the kind of statement a defense attorney might make in a trial on behalf of his client. Sure, he's a bad man, but he's not a killer.
The word yet, when used as an adverb, means that something has not occured at a particular point in time
In each of the examples, there is a connotation that the situation is likely, or at least potentially, about to change.
Most US speakers would read the example given to mean
If I were to proclaim proudly
my wife would take it ill. She expects nothing less than
Robusto's answer shows the valid present interpretation of 'is yet to be' - how can one possibly be certain what is yet to be or what someone is yet to do (unless one is a prophet).
However, there is the possibility of using the present tense to refer to a historical event or time interval:
In 1928, Hollywood is yet to be discovered by the Marx Brothers.