If Beatrice marries now Dave, do you think she will keep her title or be Mrs. Clark?
She would be HRH Princess Beatrice, Mrs. David Clark. As far as I know.
Only the Queen can take her title away through letters patent (she hasn't deprived either James or Louise of that style in my opinion) and I really don't see the Queen doing that to her granddaughter.
Will the Queen give Dave an Earldom? Lets look at the recent history
Princess Margaret marries Anthony Armstong-Jones - he accepts the Earldom of Snowdon.
Princess Alexandra marries the Hon. Angus Ogilvy - he declines an Earldom.
Princess Anne marries Captain Mark Philips - he declines an Earldom.
We have to look back to Princess Margaret to see a man marrying into the royal family and accepting a peerage - so nowadays it's a fairly archaic practice - but we know how Andrew loves the baubles of royalty.
By the way, can I point out that in my opinion the title of this thread is a complete misnomer - the BRF aren't really modernising at all.