It is odds that he will come.

这个表达不是很规范。

It 是形式主语， that he will come 是真正主语。odds 是形容词用法，大致等于 possible, likely。相当于：

It is possible that he will come.

It is likely that he will come.

网友说的是 odd 的名词用法：

《牛津》 usually the odds

（事物发生的）可能性，概率，几率，机会 

the degree to which sth is likely to happen

The odds are very much in our favour (= we are likely to succeed) .

我方胜算的几率极大。

The odds are heavily against him (= he is not likely to succeed) .

他成功的几率很小。

The odds are that (= it is likely that) she'll win.

她有可能会赢。

What are the odds (= how likely is it) he won't turn up?

他不会露面的可能性有多大？