I would not mind if UA backtracked out of miles not expiring and instead did something similar to what Accor does with their loyalty program, which is to continually extend the expiration of your points to be one year from the completion of your last booking. Having miles never expire does not dovetail with building brand loyalty. However, that is one pandemic-era benefit that optically is going to be hard to pull away, I would think (and not one that strikes me as UA wanting to be a 'leader' on).