In germany, a Leopoldina-paper has been published recently. It's basicly a suggestion for the goverment how to deal with the situation in the future, written by a group of experts.
They suggest to try to return to a somewhat normal life soon, with staggered openings for schools, restaurants and public places. They also suggest to maintain distance, and where not possible, masks.
So technically, IF the goverment decides to follow the paper (and Angela Merkel is very likely to do so, as she likes to wait until it is clear what is considered the best solution), theme parks might be able to open soon, with a mandatory facial mask for every guest, and some restrictions for food outlets, so people keep their distance while eating. I think this would be possible if the parks open up with a limited capacity - by limited I mean in a way that restaurants and snacks don't become overcrowded, but the park can still be decently filled with people and should be able to earn some money.
The paper also suggest to keep workers at home if possible, so home office is still strongly encouraged to relieve public areas of unnecessary amounts of people.
In my opinion, the suggestions sound really good. They would allow people to live a somewhat normal life again, and allow cinemas, restaurants and also theme parks to get some customers. I'd certainly prefer visting theme parks with a face mask over an opening in July.
@SimonProD The easiest way would be, if the parks hand out marks which they deem safe. The straps are usually expandable, and should therefore not become loose. In addition, a mask weights not much, so even strong g-forces should not be able to move it away - and the wind from the front will only push it closer to your face. Most rides can be ridden with glasses, those should be safe with a mask as well. The ones which are more intense should also be safe when the masks fits your face - this might have to be checked in some way.