My primary hurdle with straight value for value (defined as: user chosen amounts and typically in more frequent smaller payments) is there is a difficulty in determining the market reference price as a payer - basically what something costs without similar reference products/items.

You often have no reference point and don’t want to over pay or under pay - which creates friction. You also lack context around what the amount you choose means to the payee - patron subscriber goals help materialise what future support levels mean to a creator for example.

Sometimes you could calculate based on how much of your time was saved. That doesn’t really work for entertainment content.

Ultimately I think peer to peer payments to more directly support causes, communities, and individuals will grow significantly - perhaps just with more structure than ad-hoc zaps.