From what I understand of ENIAC, it had a very large number of manually-operated rotary switches which behaved as ROM. While programming ENIAC in the early days required a plugboard, the machine was eventually enhanced to allow it to be programmed entirely via the switches. The speed at which the machine could change programs, however, was limited by the need to have operators manually set all the switches.
Given that electronic information storage was bulky, hot, and power-hungry compared with mechanical switches, it would seem like it should have been possible to construct mechanically-set electronically-read storage elements which could be read electronically just as fast as the manually-operated switches, but whose state could be set via automated electromechanical means. Did any machines ever actually do such a thing, or did magnetic core memory become available soon enough to make such an evolutionary step unnecessary?