I think I know the article that you are thinking of, and from what I remember the issues were in getting the dirt composition correct and making sure that it wasn't too wet or too dry (I remember Tropicana Field was mentioned and that the dirt infield would dry out too quickly).
I have been in engineering for over 30 years, and the idea that providing drainage for 5,000 square feet of grass is a major challenge is very puzzling to me. Surely providing drainage to an outdoor field that can get major rainfall is more of a problem than in an enclosed stadium, and it has been done for outdoor fields countless times in both major sports parks and small municipal sports fields.
I think Yorkshire Blue Jay summed up the issue previously in the following post:
His point seems to be more along the lines of what is the point of doing a spot trial when the technology is already known. However, in my opinion, if 40 - 50% (to pick a number) of baseball action occurs within the boundaries of the dirt infield and a hypothetical grass infield diamond then "why not?". I am not sure that this would even have a major impact on other uses of the Rogers Centre; couldn't most other uses occur on the artificial turf?
PS: The pictures above already demonstrate that removing the concrete floor is no challenge at all.