Hola Alexander,

In this structure that you mention, the second part of the sentence would be referring to something happening in the present despite using the past tense, or actually something happening in the past.  For example, I could say:

"¡Quién iba a pensar que Marcos tenía novia.!"

Who would have thought that Marcos had a girlfriend!

Who would have thought that Marcos has a girlfriend!

Or I could say:

¡Quién iba a pensar que Marcos se había casado!

Would would have thought that Marcos had got married!

In the first sentence with "tenía novia" we can be referring to him having a girlfriend at the present time, or could be referring to him having a girlfriend at some point in the past and he doesn't have a girlfriend anymore (maybe...)

In the second sentence using the pluperfect (se había casado)we are clearly referring to something he did/had done in the past.

But coming back to the first sentence and changing it to something different, for example:

"¡Quién iba a pensar que Marcos se casaba!"

we are referring here to something that Marcos is going to do (despite using the imperfect casaba), still to happen.

There is a lot of flexibility with this structure.

In terms of using the present, yes, I think you can, for example:

¡Quién iba a pensar que Marcos se casa mañana!

¡Quién iba a pensar que Marcos tiene novia!

So, most of the time you need to know the specific context to really know if they are referring to the present, past or future.

I hope this helped a bit.

Saludos

Inma