This is a smart way of doing it, I think.

But if you start reliably auctioning off upgrades at cheap rates (which EY seems to be doing now), there can be significant second order effects from that, e.g. people not booking biz tix anymore in the first place. For each person who decides to buy an economy ticket instead of a biz ticket, you probably need five paid upgraders to compensate. I think the viability of the biz cabin can be at risk.

And, of course, as an Elite flyer, I personally do not like at all that airlines start selling those remaining seats instead of operationally upgrading me.