While "Evergreen" is the goal, eventually the financial needs of WotC will necessitate a new edition (since core books are the primary income of any RPG).
I'm not sure about this assertion. Hasbro doesn't put out new editions of Monopoly or Life with changes to the core rules, they just dress them up in a new skin every once in a while. They don't spend money on development, just on marketing and sales. D&D could follow that path, needing only enough sales to new players to cover those costs. As long as they maintained a healthy market share, there would be no reason to create a new edition.
If sales really drop, it wouldn't mean putting out a new edition, it would mean dropping supplement creation down to 1 every year or three. If it's popularity picked back up, they could go back to three or four per year.
If Hasbro wants D&D to be a game played through generations like Monopoly, Risk or Life, they can't keep reinventing it every 5-10 years. And the bottom line is the minor flaws in the current system are vastly outweighed by the ease of use of the system and it's accessibility to casual gamers, who are driving sales year after year after being introduced to the game, having fun playing a Life cleric with a pig and the actor feat and then buying their own PHB.
Ideally this would come as 5.X versions that are backwards compatible (as 2E was originally supposed to be for 1E), so that non-core books are still relevant.
I could see very minor changes made in the future to the core books. Perhaps a feat added or dropped here or an additional version of a class there. Maybe a "Complete" Players handbook that at some point consolidates all of the class and feat options. But no core rule changes. Nothing that would mean that someone with an original PHB wouldn't have the same mechanics for as someone with a PHB printed in 2030.
And they certainly won't call it 5.x on the cover. Sure us hardcore fans will notice and discuss it, but to the public, it will still just be the D&D PHB. They don't even brand 5e on the cover of the core books now.