After China has built the first all DC city, during the half century that we in the U.S. are weaning ourselves from 60 Hz AC, 60Hz transformers will not be constructed by present customs. Rather, they will be switching power emulations. These emulation transformers are completely within the present state of the switching art. The technology will not use much clocked pulse width modulation, though clocked 100% duty cycle, may prevail over hysteretic loops. Integrated circuit manufacturers and ferrite core designers are walking us up a box canyon.
I am not a complete convert to a massive DC power grid. I think local grids can take advantage of this with the drawback of sustained arcing. Certainly high voltage DC can be transported over long distances as efficiently as AC. With the presence of active transformers, perhaps makes the grid more vulnerable to adverse operating conditions such as lightning strikes, solar storms, etc. The active transformers may need to be bidirectional for energy sharing purposes. The DC grid could be much more smart as far as load sharing, more graceful degradation, and better interoperability with the renewable energy DC sources. Long term, these problems can be solved, but in the medium term, they can present some problems some of which we can foresee and those we have not dreamt about yet. In reference to computing power and the loss of individual privacy, but is also appropriate for all technologies: "If it can be done, it will be done."
Aside, iron wire is a very intriguing idea for its use as a core material. Obviously, the alloys need to be played with to improve its wider frequencies of operation. But it is very do-able and its use would be flexible as to choosing the number of core turns needed for each power application. This is especially intriguing for balanced flux applications such as forward-mode transformers.
I personally have no experience with iron wire, just some iron cores. Perhaps others have more experience with iron materials and iron wires. Its price, availability, and more buy-able lengths will change drastically as its varied demand changes. Keep us updated on your experiences in this area. This could be a life-changing event for the power field.