Is there a way to use it only for these "critical" to deliver emails?  I'm fine for the rest of our notifications and other emails to be internal.  This would allow us to use a very reliable service for those emails and our IP/server for the rest.  This would be cost beneficial as well as ensuring critical emails get delivered.

I think the idea is good in itself, to split up email delivery methods based on type of email, but its not something built in natively. Its one sending method and that's it. 

The cost factor is why I switched to AWS SES.

Feature suggestion?

This would help ensure delivery of the most important emails.  And cost less than forcing ALL emails including status updates and post alerts  to go though a formal service.