It can be that...这样的句子，除了刘老师所说的it为人称代词，指代前文提及的内容，that为表语从句外，确实还有另一种情况，即it为形式主语，can be中的be为不及物动词，意为exist 或 happen，that引导的是真正主语从句。can表示可能性，can be 这种情态意义可以改用is possible替换。即 It can be that... = It is possible that...。it为形式主语，that引导外置主语从句。以下二个句子来自COCA语料库。仔细读这二段文字，我们会发现，it can be that...句子中，it并没有指代前文任何内容，it只是一个虚指主语（形式主语）。

If a country is losing a creative young generation, they have not had the means to reproduce itself. This will be a vicious cycle of degradation, of decline of the society. It's not just a problem. It's the most difficult problem that Greece is facing today.  I call this the annihilation of a generation. They have no jobs. They will not have a generation of creative entrepreneurs in Greece. It can be that Greeks and the Greek society will decline totally, as a failed state, as a failed society.

 It is also true that not everyone can be a disciple, since discipleship also presupposes a special call from Jesus. It does not depend on the will of the individual. It can be that someone wants to follow Jesus but is not made his disciple.

网友给出的以下二个词典例句中，it也是形式主语，that从句为真正主语从句。can be可以改写为is/was possible, 意义相同。

Could it be that it was written wrongly?  

= Was it possible that it was written wrongly?
 《新英汉大辞典》

It could well be that he has a real vocation. 

It was really possible that he has a real vocation.

对于it can be that...的这种理解可以圆满地解释as can/could be这种比较结构。例如：

He ran as fast as could be. 比较分句补全后为：

= He ran as fast as it could be that he would.

= He ran as fast as possible.

= He ran as fast as was possible.

= He ran as fast as it was possible that he would.

即as分句省略了形式主语it和外置that从句。