So, there are a few things you listed that simply would not work. The biggest being that there is no point in exhibit expansions for orcas anymore, as orcas are a phase-out species for all SeaWorld parks. Last time a tank expansion was attempted, something like what you mention was allowed, with multi-level viewing and all, even a full current to run through the exhibit. It was allowed with the condition no breeding was allowed. SeaWorld decided to phase out orcas entirely after that decision.
I really hate to say this, but there is no point to doing a full-scale renovation of an exhibit for what is more or less a phase-out species in SeaWorld's eyes. California law prohibits it, and a very strong animal rights campaign has turned the public strongly against cetacean captivity entirely (and I guarantee elephants will be next, but that's a whole other discussion). At best we can possibly see modifications to the exhibits, but unless new management is drastically different, that's about it. If we are looking at what orca exhibits can be, we must turn our eyes to Spain, where Loro Parque has a renovation planned, China, where new marine parks are being built, and possibly (but doubtfully) France. SeaWorld has given up entirely at this point. Incidentally, do look up Marineland Antibes. There's no official size for their enclosure, however, that might be what you look for when you say you want a lake-sized enclosure.
Now, as for the dolphin exhibits, I recommend you look at SeaWorld Orlando and SeaWorld San Antonio's newly remodeled dolphin exhibits, or Discovery Cove, a separate park they own. I agree fully with you that SeaWorld San Diego needs a similar renovation, but they would have to go through the California Coastal Commission, who, as I mentioned, has already proven to be a problem. I think the coral reef thing is a really, really good idea. SeaWorld still builds new aquariums, but they're all more like zoo aquarium buildings, none of them really have impressive individual exhibits. A giant coral reef tank would be an excellent offering.
Finally, I don't know how much you know of SeaWorld's current goings-on, but in San Diego the dolphin and orca shows are now very educational. It sadly has not worked.