Will lack of backlighting cause difficulties tho?
Being able to change the sign quickly/often for new advertisers might also bring in more money. E.g. you can now sell different advertisements on Friday versus other weekdays, and more specialized Christmas advertisement.
Counterpoint - a large e-ink advert market means (likely) cheaper e-ink products for consumers. E-ink isn't likely to replace cheap paper, it's more likely to replace LCDs and OLED screens which are already more obvious/intrusive as they're self-emitting.
In theory, the big screens could be roughly comparable to LCD screen prices, like the 6" e-ink screens already are.
They key cause of cost in e-ink is lack of demand, and more specifically lack of demand compared to LCDs. LCDs are produced at a rate of billions per quarter, they're so stupidly cheap it's almost unfair to compare them with e-ink. Point is, LCDs will always be cheaper unless demand changes.