The future will always be bigger, farther, faster.
Gulfstream has validated that by taking the G650 a bit farther with the ER. Then there's the Global 8000....
Gulfstream's newest products, the G500 and G600 are merely long overdue replacements for the G450 and G550. Both of which will be "greener and more comfortable" than their predecessors. But still not as long or as wide as the G650. They'll fit their respective niches by design, as intended.