For me to take a company seriously MFA must be in all their plans. MFA is not an enterprise hook for upsell, it is a fundamental requirement for any online service these days.
Especially in a security focused product.
Not offering MFA on the free tier tells me you're more interested in making money than in security.
There are plenty of other features that an enterprise will pay for.
It would be good to offer SMS MFA in the free tier, providing the dev plugs in valid Twilio credentials.