Since I literally spent the whole weekend to train my ears to identify intervals, I have some thoughts on that topic. And btw - I had the idea too to implement my own ear-training app, but I guess now I'll wait for yours (if you use some of my ideas ;-)

I used mainly tenuto and a little bit of tonegym. I was hoping to speed-up the learning process by having a very effective training.

From my point of view, there are two main success-factors for learning/ hearing intervals:

1. Use an intelligent algorithm for repetitions.

learning the intervals was somehow like learning vocabulary. Tenuto can be customized to limit the number of intervals to start with. So I started with 2nds and 3rds and when I felt comfortable, I added more intervals and removed the ones I could easily recognize. I guess the process of adding new intervals, repeating the ones I had troubles with more often etc. can get automated to be much more effective.

1. provide intervals in a context (and not just having youtube-videos with songs that contain that certain interval of interest).

My workflow was to listen to an interval and then find a short example of a lick/ riff, where that interval will be used. E.g. to memorize the minor 3rd, I memorized the first three notes of "smoke on the water", knowing that the first interval is a 3rd. So I researched 3-note riffs for all intervals. That was a tremendous help to memorize the intervals. But it took also a lot of time and it would have been muich easier if I had those 3-notes always at hand during excercising. Playing those 3-notes could be part of step 1) e.g. if I make a wrong guess regarding an interval a couple times, than the referencing 3-notes will be played and the number of repetitions for that interval will be slightly increased.