I think the requirement is just fine.
I've been a HHonors member since 1987 - I've been a diamond for 18 years.
As lifetime hotel status was never in play, I had always stayed at Hilton's and Marriott's to keep status in both and to take advantage of special offers.
I am told (Why in the world do we have to ask via email??) I have 950 Paid nights with HHonors. I've also been told I had been given "legacy" status some time ago which meant I had been 4 year extensions on my Diamond status - no big deal as I always made it anyway.
When they first announced Lifetime Diamond and I was not included, I was initially put off. I quickly got over it as I'm going to make it before I retire which is all that really matters.
The Only thing that would really matter is making Diamond something special, just not a level marginally higher than Gold and a bottle of water.