I don’t see product placement as adverts or links to real world items I see digital versions of real world items, so when your character stops to drink it won’t just be glass of water it will be a bottle of branded water or maybe at higher levels it would a branded energy drink.
When you go in to towns and cities General vendors might famous convenience stores and you would buy your equipment from well know sporting goods establishments, your food could come from burger or donut chains. They could go on on like having bar tenders selling branded drinks so all the little kiddes could run round smashing stuff up while off their faces on vodka redball’s.
Why limited themselves to billboards if they could get that level of advertising in the game maybe that wouldn’t need to charge players any money subscription fees.