The closest thing to a downside I can come up with is that, at least in CA, there's more than enough solar already. Adding solar to the grid without batteries included isn't really productive.
I think that’ll rebalance over time but one of the biggest questions I’d have is how to use all of the batteries people are driving around. A buddy shifted his car charging to work because they have a convenient setup with a bunch of solar panels and that seems like a good path to encourage going forward: let sunny day over production shift vehicle charging off of times where load would need to come from grid batteries, fossil, or wind.