I'm neither against osz2 nor for it. I'm neutral on this situation.
As a player, it annoys me when the custom skin for the map, or the storyboad, makes it impossible for me to play. In this case, I delete the skin/storyboard, and there you go. It's a bad move from me because I'm denying the work from the mapper, but I want to enjoy their maps rather than hate them for something that can be so easily overcome.
One thing though, about epilepsy: for now, epileptic people can remove the storyboards that cause epilepsy and can enjoy all the maps. But when os2 comes out, if as planned players won't be able to remove the storyboard, epileptic people won't be able to enjoy all the maps, and this is a problem.
Then again, some storyboards were made to be distractive (in some approved maps for instance), and some others are a very nice addition to the map (such as
http://osu.ppy.sh/s/16008 ). Storyboards are part of the map as much as skins any the diff themselves.
However, people started abusing it, making storyboards and skins that made the gameplay not enjoyable. As for heavy storyboards and slow computers, not everyone can affort a very powerful computer that can run osu! at its full capacity. But there aren't many storyboards that are this heavy, so just avoid playing the maps.
As long as storyboards are concerned, what about collabs ? The storyboarded names are important to know who mapped what part. Although usually these storyboards are light and cause no problem, some maps have heavy storyboards on top of it, which may cause lag and be what some people whine about.
The only real issue I see coming with osz2 is epilepsy. I don't know how to fix it, but all the other issues are just people not being capable of adapting to what they face.
On a sidenote, how will modders check the content of the .osz file ?