What can be done to slow/prevent mining centralization? Assuming all buyers have access to the same ASICs (ignoring that ASICs developers and manufacturers will always have the latest first, even if only used for "testing" prior to sale) energy costs would seem to promote a long term trend of mining in areas with the lowest relative costs.

I believe in the PoW model and am not interested in PoS solutions. What can be done to slow/prevent centralization in areas with the lowest energy cost?
Asking how to prevent the mining industry from being centralized into places with low electricity costs is like asking how to prevent the shipping industry from being centralized into cities that are on the coast.  Both industries will tend to thrive in places where the profit margins are highest...and there's no profit margin in building a port in a land-locked city.

Since we are assuming that access to the latest ASICs is uniform for all contenders, profit margins are determined by electricity costs.  However, remember that running the ASICs isn't the only thing that miners do that costs electricity.  Cooling the ASICs is probably the larger electricity cost, just like it is in most data centers.  Given two locations with the exact same electricity cost, but different average temperatures, the location with the colder temperature would prove to be more profitable.  It would cost less electricity to cool the ASICs.

Now the problem seems to be mining centralizing into locations that have both low electricity costs and low temperatures.  However, the second factor does create a variation in the trend.  There are some locations that may have higher electricity, but are so cold that they don't have to use that much of it to cool the ASICs.  There are other places that may be warm, but have such low electricity costs that it doesn't matter.

I'm fairly sure your question doesn't have a simple answer, but be reassured to know that there is at least another factor that will affect the trend.