This is fun to play around with. But, I really dislike the constant dictionary modification (per person) and different schools of theories. You end up having to toggle plover on and off every time you have to type a word that's not in your dictionary (and decide to add it or not, according to your theory so you remember how to type it). This is going to happen to you very frequently depending on the context you're typing in. It's why court reporters spend time before and after court modifying their dictionary and cleaning up their dictations.
Also, depending on where you learned English, you're going to have a lot of "is that word really pronounced like that" situations when you go to type a word the first few times.
To sum up my frustrations, want to type about 'foo' detailed subject? You're going to have to spend time adding words to your dictionary, or toggle plover off to type faster. Basically, you can type about 97% of a sentence using Plover, but you'll have to turn it off or slow down a lot to type that last 3%.
I've not used the tech, but maybe you could reduce some languages to something lower-level than words, but higher-level than letters. Like syllables. A dictionary of syllables might not be useful, if it's a 2-3 letter syllable that's looked-up via a 2 key chord. Dunno, that might be too simple. But I'd say there's a lot of space here for something better than regular stenography or QWERTY.
Much of what steno dictionaries do is just that. Here's plover's default main.json dictionary [0].
The ^ character in entries works like glue. So entries that end with ^ attach to the next thing you write, and entries that start with ^ attach to the previous thing you wrote.
You don't necessarily need to toggle plover off to write words that aren't in your dictionary. You can just fingerspell them [0]. (although that's generally not as fast as typing them with qwerty).
It's been a little while since I last touched steno now, but I don't remember running into too many words that both weren't already in the default plover dictionary and weren't possible to easily construct with existing words.
Also, depending on where you learned English, you're going to have a lot of "is that word really pronounced like that" situations when you go to type a word the first few times.
To sum up my frustrations, want to type about 'foo' detailed subject? You're going to have to spend time adding words to your dictionary, or toggle plover off to type faster. Basically, you can type about 97% of a sentence using Plover, but you'll have to turn it off or slow down a lot to type that last 3%.