I'm interested to know (if any of the regulars could say) just how many non-Japanese people visit the parks? Is it possible to spend a day at one of the parks and not see anyone else from another 'western' country?
Absolutely. But not all foreign tourists are Western, including the group of foreign tourists that many Japanese people would most like to avoid.
As for the chances of an English-language app... I guess it's possible, but I wouldn't be surprised if they never do it. For various reasons, OLC doesn't give a rat's behind whether foreigners visit their parks or not. Some of these reasons are justified & some are simply because they don't want the trouble. Foreign tourists are risky.
Japanese Social Rule #1 - Follow the rules (posted rules, spoken rules, unspoken rules, cultural rules, etc) without question, even if they don't make sense or you don't like them.
Japanese Social Rule #2 - Never make trouble for or embarrass other people.
As a foreign tourist, how do you know what most of those rules are? You don't. And therein lies the rub. Nobody will judge you for that, and certainly they're going to be kind to you because they know you don't know better, but they also don't really want to deal with it. Thus, they're not going to make it super easy for foreigners to come & they will heavily prioritize locals in almost everything. Kind of like... "you can come, but stay in your lane"
Here is an example. A while back, someone came to these boards very upset because the windows at MiraCosta cannot be opened more than a crack. She thought this rule was stupid. She wanted to know the reason for it, and sent multiple emails to the hotel asking why she couldn't open the windows. She then shared that she was relieved to have found a terrace room & no longer needed to break/jimmy the windows open as she had planned to. That is exactly, 100%, to the letter, the kind of behavior they expect from foreigners and that they don't want to be hassled by.
To be honest, as a foreigner, you could live here for 50 years & still not know all of the rules - though hopefully you would learn the language, which is 90% of the battle. The other 10% is a gap that can never be bridged. This country is no "melting pot" - it's "Japanese" & "not Japanese." TDR is a "Japanese" place & inclusivity is not a goal. It's no coincidence that Disney, a foreign company, has NO ownership stake in these parks. Just something to keep in mind the next time you wonder why OLC seems to hate you. They don't. They would just prefer you didn't bother them.