Only 2 real questions in my mind, both of which can only truly be answered over time: 1) price stability and 2) deliverability rates.
Rant: SMTP is just a bad legacy joke that should be augmented (replacement is probably not realistic) with some new API standard.
Indeed, your two questions will answer themselves over time, but we are doing everything possible to keep competitive prices. As for the deliverability rate, we have implemented several mechanisms to ensure that it remains optimal.
I agree with you about SMTP. Emails in general are a legacy joke.
This could be a show stopper for a lot of applications.
Problem is, most replacements I've seen are even worse vendor lock in. While I hate SMTP to, it being one of last open two-way long-term communication systems out there is something most of us should be thrilled with.
There is no reason that sending an email can't be done with a simple, single API call. The back and forth "dance" that SMTP requires is just an absurd waste of time. There may have been a good reason for it at some point but today, it's hard to imagine what that was.