Jason and Liz have admitted their feelings and have been open to try. However, someone or something always happened.
So, what changes this time?
Liz is heartbroken over what she did to Jason regarding the replacement baby.

She will be hesitant with Jason.
Her heart can't take anymore.
Oh, wait, my heart can't take it anymore.

I am tired of waiting.
I think I would feel better if Jason was back.

I do think the possibility of Jason fathering all of Liz's children is there.
Especially, with Hells, Dr. O and Heather Webber having experience with paternity changes.

However, I don't believe RC would or could write it well.
His love for the Spencer clan concerns me.

During Jason's absence, Jake should have returned.