UA really doesn't have an incentive to devalue MP miles below 1 cpm.

The devaluations discussed in this thread are all about moving the "fixed" value of a mile from a certain trip (which is inflationary in cpm) to a penny amount. If miles were, for example, hard-pegged to 1 cpm the number of miles required to take a certain trip would grow over time with inflation (just like cash fares). It's a natural consequence of earning being pegged to revenue; otherwise the ratio of revenue flights to award flights would slowly decline without the "devaluations".

Would be interesting to do the analysis of how much of an award could be bought by someone doing 100k BIS miles at UA's break-even RASM over the years.