Ok, here I will give my input on why this is unlikely to happen and this assumption is gonna backfire badly on those who think this is logical.
First of all Karin is an Uzumaki. The Uzumakis are direct cousins of the Senju and were born from Ashura's side.
Sasuke is an Uchiha and the Uchihas originated from Indra's side.
If Karin and Sasuke had Sarada as a child, then this would mean that the Ashura Lineage and Indra Lineage have fused together.
It's manga fact, that Ashura + Senju = Rinnegan = Hagoromo's power.
This would mean that Sarada would eventually awaken Rinnegan and come close to Hagoromo's power.
This would make Sarada very overpowered especially in comparison to Bolt. This would break the Yin = Yang theme and it's not gonna happen.
Even if it happens, it's a 100 % gaurantee that Sarada will neg Bolt Laughable Diff. Rinnegan + Hagoromo's Body + Large Uzumaki Chakra Reserves, please.