Would ITV be willing to put Emmerdale/Corrie on there a day ahead of the ITV broadcast, or more likely a BritBox specific "straight to video" style special.
I just can't see it taking off really - I don't get round to watching most things on Netflix, Now TV, Amazon Prime or indeed the BBC iPlayer, so aren't going to add another to the mix. ITV aren't really going to have much to offer beyond what they offered on Encore, though I guess they could leverage the power of Love Island and put the international versions and former seasons on there. A bold thing would be to put their winter season there (as CBS did one year with Big Brother when launching All Access), but even ITV aren't going to risk what is their biggest cash cow at the moment for a fledgling service.
They also of course have to get the service out there too - even if it will be available via Freeview Play, Sky and Virgin Media I suspect it won't be added to older Smart TVs.
Stay Home. Protect the NHS. Save Lives.