1. Why using this modal: will; why not You might have ... ?
2. Why is there a question mark at the end; why is it not a full stop?
3. Why using present perfect continuous? why not You should be doing or should do ... .
4. What tense is it?
1. You would have to ask the person who said it why they chose this wording!
You most likely haven't heard of me before is an approximate equivalent.
You may/might not have heard of me before is also very close.
2. I don't know. I would have used a full stop.
3.
should do is advice for the future.
should have done is a mild reprimand for 'not having done' in the past.
should be doing spans the time just
before the present and just after, including and surrounding the
present, so is usable as either a mild reprimand for 'not doing' in the
past or advice for the future, or as both, more or less combined into one idea.
should have been doing spans the time
surrounding some past time in a way analogous to the previous
description. But because it was in the past, it can't be advice
for the future (counting from the moment the words are uttered). It is as if it is saying, if I had known about
this at that time in the past I would have said,
... should be doing, i.e., I would have given a mild reprimand that you had 'not been doing' and advice for (what was then) the future.
4. The main verb carries the tense.
were is past.
CJ