> Now we're talking about downloading iPhone apps that promise 10% more speed

That doesn't sound like anything I've ever heard of. Many manufacturers require expensive subscriptions to access service manuals and programming software.[1] The average person (and even a lot of small-time mechanics) doesn't have access to those resources.

[1] http://www.nastf.org/i4a/pages/index.cfm?pageid=3291

ECU flashes don't require much more than software and the right kind of cable.

You haven't heard of it because it's too stupid and dangerous to allow to happen. But it's a natural consequence of car ownership including read-write access to its computers.

Many cars have had externally reprogrammable ECUs since the mid 1990s (with lots being fully reverse engineered), but yet tuning is still relatively esoteric and generally very expensive.

What do you think has changed / will change that will lead to an onslaught of dangerous amateur tuning by phone? The technology to do so has existed for years.

It exists in other motor vehicles. My last roommate had a quad where he would tune the ECU with software on his laptop depending on where he was riding and what parts he had installed.

Falling barriers. Like you say, tuning is currently very expensive. The financial and technical costs act as an idiot filter (forgive my negativity.) Those barriers are falling so we're left with artificial costs i.e. legal penalties and intentional code obfuscation.

Huh? I knew kids in high school who could barely read who could tune old cars without much of a problem.

Now you need a computer, hard to find software, special cables, etc.