It's a good idea to think of a converse situation, but this is a bad example. The constraint was not about technology but about budget, perceived benefits and political will.
What technologies existing in 1969 might have been used to create an environment with a breathable atmosphere and a self-sustaining ecosystem on the Moon?
What technologies existing today might be used for this purpose, assuming no financial or political limitations?
What technologies existing today might be used for this purpose, assuming no financial or political limitations?