We absolutely would not need eminent domain. The city is full of tenantless low-density buildings close to transit hubs where the owners would voluntarily build six-story apartment buildings if we allowed them to.
(If they wouldn't, then why did it need to be forbidden?)
Appeals to Paris and vast tracts of six-story apartments as an alternative to high-rise construction are dangerous because they create the illusion that a six-story height limit is okay. If we could build the whole city over again tomorrow, it might be. Today, recognizing the reality that most existing low-rise structures are in it for the long haul, when there is an opportunity to build, every floor counts.
(If they wouldn't, then why did it need to be forbidden?)