Yes - they'd have to fully test each app under a variety of circumstances, and then they;'d have to continually retest every time the app is updated. And have you seen already just how many requests there are? Everyone has a favourite player or app. So all of a sudden the whitelist grows to 40-50 apps, and FiiO simply doesn't have the developers to keep everything updated.
Then what happens with a multitude of apps which they aren't controlling? Word gets out that they don't care, that they have poor quality and service. And everyone misses the point:
- The M9 runs on an Exynos chipset to provide longer life.
- The M9 is very fast as long as you use the apps which are created for it specifically, or ones they've tested and found to be suitable
- The M9 is not a full Android experience - it was never intended to be. FiiO stated it in their documentation, on their website, and on this forum. If you want full android and all the flexibility it offers, you bought the wrong device. But if you do want that plus the other features FiiO brings, you're going to need to pay a lot more for the product you're looking for.
The M9 wasn't ever intended to be a Swiss Army Knife of audio, and it is what it is. Personally I think its pretty good - but then I don't expect it to be something its not.