Serious thoughts now; physiologically, it would, as several posters have noted, be very difficult for a woman to play at the very top level of the mens game. It is not impossible though - at least, not for a wicketkeeper (where the role, largely devoid of power based exertion, is most closely suited) - or perhaps for a top order batsman/woman (never quite worked out how that should be phrased) where, at least in first class cricket, their lack of power should not be that relevant because for the most part they are looking to bat time.
It is not correct to say that females players have never succeeded in mens premier league cricket - Aaron Brindle made a century (admittedly in one of the weaker premier league structures) and Clare Connor was moderately successful in Sussex. The step up from ECB PL to County 2nd XI is nowhere near as big as some people seem to think - its a step rather than a leap. So the question is, where would the top levels of Womens cricket sit comparatively? I reckon women's test cricket is about the same standard of good men's league cricket.
There have probably been two players I'd say could make the transition in my time watching the game. Clare Taylor is one - she was a quality bat with exceptional technique, and would cope with most male bowling, even if she didn't score quickly. The other is Sarah Taylor - again, aside from her keeping, she has the technique with the bat that she should be able to cope (with the appropriate training beforehand).
Do I agree that she should be allowed to? No. Nothing sexist involved - I just think that women's sport struggles for credibility at times as it is, and the chances are that the blurring of lines will hinder rather than aid development. I'm also a tad unsure about some of the, erm, issues in professional sports that might be touched upon - for example, sledging...