I'd think that the Lifetime D+ population isn't that large so there wouldn't be a great number of extra people in the First Class Lounge to make a noticeable difference in usage. The Business Suite lounge is only a rebranding since they're still the same as before OZ dropped First to Business Suite.
Who know what the Korean FTC will say but it just doesn't make sense for KE to play around with this until they finish with the final merger stuff and the next rebranding exercise. .