"We are seeing players having more power and more options than ever before, and we will certainly see many more players opting to go down this route,'' one English county executive said.
White ball-only contracts generally aren't worth as much as those for players available and chosen for all forms of the game.
Nottinghamshire won both white-ball trophies in England last year, with Hales scoring 434 runs in the one-day competition at an average of 72.33, including 187 not out in the final.
A new eight-team T20 competition is due to start in 2020. That is likely to sharpen the focus of both players eyeing an opportunity, and counties figuring how to spend their money.
In New Zealand, fast bowler Mitchell McClenaghan, who has fashioned a highly impressive T20 career, stepped away from a New Zealand Cricket Contract this year — while still available for selection — to free himself to take up any T20 franchise work around the world.
Blockbusting opener Colin Munro is known to have at least pondered the idea before sticking with New Zealand, to terrific effect this season.
■ New Zealand spinner Mitchell Santner and fast bowler Neil Wagner have taken up English county deals this year. Santner is heading for Derbyshire while Wagner, who only plays test cricket for his country, is returning for a second term with Essex and will play all three forms.